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'Climate Change: Information on Three Air Pollutants' Climate 
Effects and Emissions Trends'
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Report to Congressional Requesters:

April 2003:

CLIMATE CHANGE:

Information on Three Air Pollutants' Climate Effects and Emissions 
Trends:

GAO-03-25:

GAO Highlights:

Highlights of GAO-03-25, a report to Congressional Requesters, House 
of Representatives

Why GAO Did This Study:

Solar radiation is absorbed by the earth and is subsequently 
reemitted. The buildup of carbon dioxide and certain other gases in 
the earth’s atmosphere traps some of that radiation. This is known as 
the greenhouse effect and is believed to contribute to a warming of 
the earth’s climate. Concerns are growing that, in addition to carbon 
dioxide and other conventional greenhouse gases, certain air 
pollutants may affect the climate.

GAO was asked to examine (1) the extent of agreement among scientists 
regarding the effect on the climate of three air pollutants—black 
carbon (soot), ground-level ozone, and sulfate aerosols—and (2) seven 
countries’ efforts to control these pollutants, trends in these 
substances in these countries over the past 2 decades, and estimates 
for the next decade. GAO was also asked to summarize the relationship 
between economic growth and environmental pollution.

The seven countries include four that are economically developed—
Germany, Japan, the United Kingdom, and the United States—and three 
that are developing—China, India, and Mexico. These countries were 
chosen because they have large economies with a high potential to emit 
these pollutants.

The two federal agencies asked to comment generally agreed with the 
information presented in this report.

What GAO Found:

Scientists generally agree that sulfate aerosols have a cooling effect 
on climate, while ozone in the lower atmosphere has a warming effect. 
Black carbon tends to warm the atmosphere but cool the earth’s 
surface. Sulfate aerosols also affect how much and where it rains. 
Considerable uncertainty remains about the size of these effects.

All seven countries are taking steps to reduce the amounts of the 
three pollutants. The four economically developed countries have well-
established efforts underway. In these countries, the amounts of the 
three substances generally declined over the last 2 decades and are 
expected to decline over the next decade. In contrast, the three 
developing countries’ efforts are less well established. In these 
countries, the amounts of the three substances generally increased 
during the years for which information is available. GAO found few 
projections for these three countries.

An extensive body of research has examined the possible connection 
between economic development and environmental pollution, but the 
results of this research are inconclusive. Researchers also caution 
that economic growth by itself may help support environmental 
improvements but is not, by itself, sufficient to ensure them.

www.gao.gov/cgi-bin/getrpt?GAO-03-25.

To view the full report, including the scope and methodology, click on 
the link above. For more information, contact John B. Stephenson at 
(202) 512-3841.

[End of section]

Transmittal Letter:

Results in Brief:

Background:

Scientists Agree on the Overall Direction of the Three Pollutants' 
Climate Impacts, but the Estimates of Impacts Contain Significant 
Uncertainties:

The Three Pollutants Are Generally Declining in Economically Developed 
Countries, but Not in Developing Countries; All Seven Countries 
Are Acting to Reduce Emissions:

Studies of the Effect of Economic Growth on the Environment 
Are Inconclusive:

Conclusions:

Agency Comments:

Appendixes:

Appendix I: Scope and Methodology:

Appendix II: Programs and Measures to Reduce Emissions of Sulfur 
Dioxide: 

Appendix III: Programs and Measures to Reduce Emissions of Black 
Carbon or Particulate Matter: 

Appendix IV: Programs and Measures to Reduce Ground-Level Ozone: 

Appendix V: Summary of Results of Selected Studies on Economic Growth 
and Environmental Pollution: 

Appendix VI: GAO Contact and Staff Acknowledgments: 

Tables: 

Table 1: Comparative Statistics of the Seven Countries Reviewed:

Table 2: Results of Selected Studies of Economic Growth and 
Environmental Quality:

Figures:

Figure 1: Sources and Estimated Mean Atmospheric Lifetimes of Selected 
Substances Affecting Climate:

Figure 2: Direct Effects of Several Substances on Climate Change as 
Reported in the IPCC's Third Assessment Report, 2001:

Figure 3: Sulfur Dioxide Emissions in Four Developed Countries, 1980-
99:

Figure 4: Projected Sulfur Dioxide Emissions in Four Developed 
Countries, 1990-2010:

Figure 5: Sulfur Dioxide Emissions in China and Mexico, Selected 
Years:

Figure 6: Black Carbon Emissions in the United States, United Kingdom, 
Germany, and Japan, 1980-96:

Figure 7: Black Carbon Emissions in China, India, and Mexico, 1980-96:

Figure 8: Annually Averaged Global Ozone Concentrations at 5 
Kilometers, Parts per Billion, 1990:

Figure 9: Projected Annually Averaged Global Ozone Concentrations at 
5 Kilometers, Parts per Billion, 2025:

Figure 10: Number of Areas Exceeding the Ozone Standard, United States 
and Germany, 1990-2000:

Figure 11: Hypothetical Inverted U-Shaped Curve, Showing Relationship 
Between Per Capita Income and Environmental Pollution:

Figure 12: Estimated Turning Points Found in Selected 
Studies of Particulate Matter, Sulfur Dioxide, and Carbon Dioxide:

Abbreviations: 

CLRTAP: Convention on Long-Range Transboundary Air Pollution:

EIA : Energy Information Administration:

EPA: Environmental Protection Agency:

EU: European Union:

IPCC : Intergovernmental Panel on Climate Change:

UNFCCC: United Nations Framework Convention on Climate Change:

Transmittal Letter April 28, 2003:

The Honorable W. J. (Billy) Tauzin 
Chairman 
Committee on Energy and Commerce 
House of Representatives:

The Honorable Joe Barton 
Chairman, 
Subcommittee on Energy and Air Quality 
Committee on Energy and Commerce 
House of Representatives:

The Honorable James C. Greenwood 
Chairman, 
Subcommittee on Oversight and Investigations 
Committee on Energy and Commerce 
House of Representatives:

Carbon dioxide and certain other gases in the earth's atmosphere trap 
the sun's heat and prevent it from escaping back into space. This 
phenomenon, known as the greenhouse effect, tends to warm the earth's 
surface; the gases that cause it are called greenhouse gases. Most 
scientists agree that a change in the earth's climate could have wide-
ranging effects on economies, ecosystems, and human habitation. Climate 
change could make some locations unsuitable for growing traditional 
crops, which could lead to economic disruptions, especially in 
agricultural economies. However, warming is not the only issue of 
concern with respect to greenhouse gas emissions. A buildup of such 
gases could also alter precipitation patterns, causing some areas to 
receive more rain and others to become drier. Extreme events, such as 
drought or floods, could become more frequent. In addition, if climate 
change causes sea levels to rise substantially, low-lying areas might 
become uninhabitable, forcing the dislocation of entire populations. 
Evidence suggests that climate change is the result of both human 
actions (such as fossil fuel burning) and natural phenomena (such as 
solar variability). However, according to an international panel of 
experts, most of the warming observed over the past 50 years is 
attributable to human activities.

In recent decades, concentrations of greenhouse gases have built up 
in the atmosphere. Concerned about these increased concentrations, 
the United States and many other nations entered into a treaty to 
stabilize atmospheric concentrations of greenhouse gases at levels that 
would prevent dangerous human interference with the climate system. 
The United States ratified this treaty, the United Nations Framework 
Convention on Climate Change (UNFCCC), in 1992. Of the gases covered by 
the treaty, the most important in terms of contribution to warming, 
are, in declining order of emissions levels, carbon dioxide, methane, 
nitrous oxide, and three types of synthetic (manufactured) gases.

In addition, scientists have recently intensified their efforts to 
study the climate effects of substances not included in the Framework 
Convention. According to a 2001 comprehensive review [Footnote 1] of 
scientific research on climate change, additional substances--
generally regarded as air pollutants because they can damage human 
health and the environment--can also affect the earth's climate. Among 
the substances are the three treated in this report, listed below. Of 
these three, sulfate aerosols exert the greatest influence on climate.

* Sulfate aerosols are produced when sulfur dioxide gas is transformed 
through oxidation [Footnote 2] in the atmosphere into aerosol particles. 
(An aerosol is a solid and/or liquid particle suspended in the air.) 
Sulfur dioxide is produced mainly by burning coal and petroleum 
products that contain sulfur.

* Black carbon is a type of aerosol produced by the incomplete 
burning of substances containing carbon. Significant sources include 
uncontrolled or poorly controlled combustion of coal, diesel fuel, and 
biomass for heating and cooking, and by the burning of fields and 
forests. Black carbon emissions from these sources are accompanied by 
varying amounts of particulate organic materials.

* Tropospheric ozone [Footnote 3] is formed when nitrogen oxides react 
with certain other chemicals in the presence of sunlight. Nitrogen 
oxides are produced primarily by cars and other vehicles and by power 
plants that burn fuel to generate electricity. On a global scale, 
methane and carbon monoxide are also significant precursors to ozone.

You asked us to (1) assess the extent to which the scientific community 
agrees on the climate effects of sulfate aerosols, black carbon, and 
ozone, as reflected in the 2001 review, and identify important 
developments since that review, and (2) identify trends in emissions 
and concentrations of these three substances over the past 2 decades in 
the United States and six other specified countries, identify projected 
estimates in emissions and concentrations of these pollutants in all 
seven countries over the next decade, and determine each country's 
actions to reduce these three pollutants. In addition, you asked us to 
review the existing literature on the effect of economic development on 
a country's pollution levels to determine whether, as some researchers 
have suggested, there is a systematic connection between growth in 
income and emissions. As agreed with your offices, we examined the 
United States and three other economically developed countries 
(Germany, Japan, and the United Kingdom) and three economically 
developing countries (China, India, and Mexico). These countries were 
chosen because they have large economies with a high potential to 
produce the substances we examined.

To obtain information on recent research relating to the climate change 
characteristics of the three substances, we relied primarily on the 
Third Assessment Report, the most comprehensive source on climate 
science. We also contacted scientists in four federal agencies, who 
were recommended by staff at the U.S. Climate Change Science Program, 
which coordinates and supports government research on climate change. 
To learn about work subsequent to the 2001 review, we reviewed 
published work recommended by experts in the field. In obtaining data 
on emissions trends and projections, we found that data from government 
and academic sources in the United States and the other six countries 
varied considerably in terms of quality and availability. In cases 
where no other estimates were available, we used results prepared by 
leading researchers in the field. With respect to the types of policy 
measures reviewed, we concentrated on regulatory measures and did not 
include research and development programs, programs of a voluntary 
nature, emissions monitoring requirements, or programs to disseminate 
information or educate the public. We further focused on existing 
programs or programs already authorized and excluded proposed programs. 
We also excluded the policies and measures taking place at the sub-
national level (state or province level, for example), which are 
separate from, though sometimes complementary to, national measures. 
For more information on how we gathered information for this study, see 
appendix I.

Results in Brief:

The scientific community substantially agrees that black carbon 
aerosols warm the atmosphere and cool the earth's surface, while ozone 
contributes to warming the earth, and sulfate aerosols contribute to 
cooling it, according to the 2001 review, other scientific literature, 
and discussions with atmospheric scientists. However, scientists are 
uncertain about the extent of these effects. They believe that the 
level of uncertainty associated with these pollutants is moderate for 
ozone and high for black carbon and sulfate aerosols. While carbon 
dioxide and the other traditional greenhouse gases generally contribute 
to temperature and other effects at a global level, the three 
substances considered here operate on a different scale, both in terms 
of time and geography. These three substances can have effects over 
smaller distances and shorter time frames. In other words, their 
impacts tend to be more important locally and regionally, while having 
a smaller influence globally. Because of relatively rapid removal from 
the atmosphere, their impact may be felt in the short-term, as 
opposed to over decades or centuries hence. However, the effects of 
these substances are not limited to warming; these substances may also 
cause local cooling or may change local precipitation patterns. Since 
the 2001 review, other research has added to scientists' understanding 
of the effects of black carbon. For example, air and clouds over the 
Indian Ocean (which are polluted with black carbon, sulfates, and other 
aerosols) were found to absorb the sun's energy to a far greater extent 
than expected. These results suggest that black carbon, the only one of 
these substances that absorbs rather than reflects light, may play a 
more important role in warming the atmosphere than was estimated in the 
2001 review.

All seven countries are taking steps to reduce the amounts of the three 
pollutants. In the United States and the other three economically 
developed countries we studied, these efforts have been underway for 
decades. For example, these countries limit emissions from power plants 
that burn coal and other fossil fuels. They also regulate emissions 
from automobiles and trucks. In these four countries, the amounts of 
the three substances generally declined over the last 2 decades. For 
example, sulfur dioxide emissions declined in all four countries and 
black carbon emissions declined in three countries. Although sulfur 
dioxide emissions are expected to decline in all of these countries, we 
found no emissions projections for black carbon for three of them. 
Although developed countries have made progress in reducing domestic 
ozone concentrations, global ozone concentrations are likely to 
increase, owing to rising emissions of ozone precursors in other 
countries. In contrast, in China and the other two developing 
countries, emission control efforts are more recent, typically going 
back only a decade or so. As in the developed countries, these 
countries also target power plants and motor vehicles to control 
emissions. In the developing countries, the levels of the three 
substances varied. Sulfur dioxide emissions decreased in two countries, 
but black carbon emissions increased in two countries. We found limited 
information on ozone concentrations in developing countries. Most 
available data pertain to only a few major cities and is not nationally 
representative. Similarly, we were unable to find projections for 
sulfur dioxide and black carbon emissions for these countries. The 
quality of data, especially for developing countries, is uneven.

The results of empirical and theoretical research on the effect of 
economic growth on environmental pollution are inconclusive. This 
research has examined the hypothesis that pollution initially worsens 
as an economy grows, but then improves as economic growth continues and 
income rises. Empirical studies, which analyzed historical data to find 
such a relationship across pollutants, have had mixed results. 
Similarly, theoretical studies, which sought to identify how economic 
growth may affect environmental pollution, have produced various 
possible explanations but reached no consensus. Researchers agree that 
improved data and more detailed studies will be needed to identify how 
economic growth affects environmental pollution. Also, researchers 
caution that economic growth does not automatically lead to reduced 
pollution. They explain that, while economic growth may be necessary to 
provide the resources needed to protect the environment, it is not, by 
itself, sufficient to reverse environmental degradation and that 
appropriate environmental policies must follow.

Background:

Although the sun heats the earth's surface, a large fraction of the 
sun's energy is reflected back into space by clouds, ground surfaces, 
ice, and water. However, certain gases in the earth's atmosphere, such 
as carbon dioxide and methane, trap some of the sun's heat and prevent 
it from returning to space. The trapped energy warms the earth's 
climate, much like glass in a greenhouse. Hence the gases that cause 
this effect are often referred to as greenhouse gases.

In response to potential environmental problems linked to the emissions 
of various heat-trapping gases, the United States and many other 
nations in 1992 signed a treaty aimed at limiting climate change 
induced by human activity. This treaty, called the United Nations 
Framework Convention on Climate Change, seeks to stabilize atmospheric 
concentrations of greenhouse gases at levels that would prevent 
dangerous human interference with the climate system. Under the 1992 
convention, the United States and other parties generally agreed to 
implement programs aimed at reducing their emissions of greenhouse 
gases not covered by another treaty, the Montreal Protocol. [Footnote 4] 
The most important of these warming gases, in declining order, are 
carbon dioxide, methane, nitrous oxide, and three types of synthetic 
(manufactured) gases--sulfur hexafluoride, hydrofluorocarbons, 
and perfluorocarbons.

In recent years, scientists have focused increased attention on the 
climatic role of certain substances that are regarded as air pollutants 
(because of their harmful effects on human health and the environment) 
but are not covered by the Framework Convention or Montreal Protocol. 
These substances are aerosols (including sulfate aerosols and black 
carbon) and tropospheric ozone. Scientists have long recognized that 
these pollutants can affect climate, but these pollutants were not 
included in the Framework Convention. Sulfate and black carbon aerosols 
differ from traditional greenhouse gases, such as carbon dioxide and 
methane, in two key ways. First, unlike the traditional greenhouse 
gases, which are evenly distributed throughout the atmosphere and have 
global impacts, the effects of sulfate aerosols and black carbon are 
greatest near their sources, although they can have global impacts. 
Second, whereas traditional greenhouse gases can remain in the 
atmosphere for tens to hundreds, or even thousands, [Footnote 5] of 
years, sulfate aerosols, black carbon, and ozone remain in the 
atmosphere for much shorter time periods. Figure 1 shows the sources 
and estimated mean atmospheric lifetimes of various substances having 
an impact on climate.

Figure 1: Sources and Estimated Mean Atmospheric Lifetimes of Selected 
Substances Affecting Climate:

[See PDF for image]

[End of figure]

[See PDF for image]  

[End of figure]  

[A] Wetlands are a natural, as opposed to man-made, source of methane. 
We list them here because wetlands are the largest single source of 
global methane emissions.

[B] The lifetime of carbon dioxide depends on rates of absorption by 
oceans and vegetation.

Notes: For each substance, we depict only the most important sources. 
Additional sources of emissions exist for most of the substances listed 
above.

This graphic was prepared by GAO with lifetime data reported in IPCC's 
Third Assessment Report, 2001. Source data reported by EPA, National 
Air Quality and Trends Report, 1999; EPA, Inventory of U.S. Greenhouse 
Gas Emissions 1990-2000; and Elaine Matthews, "Global Methane 
Emissions: Historical Trends, Controlling Factors, and Future 
Prospects," in Air Pollution as a Climate Forcing: Workshop 
Proceedings, May 2002.

* Sulfate aerosols are created when sulfur dioxide emitted from, for 
example, coal-and oil-fired power plants, is oxidized in the 
atmosphere. Atmospheric sulfate aerosols have been associated with 
significant effects on public health and visibility impairment, and 
when they are deposited on earth, they contribute to the acidification 
of lakes, streams, and forests. Sulfate aerosol particles also have 
major effects on clouds, where they provide additional nuclei around 
which cloud droplets form. This can increase the cooling effect of 
clouds and may also increase the life spans of clouds. Both developed 
and developing countries burn coal to generate electricity, leading to 
emissions of sulfur dioxide.

* Black carbon, a type of aerosol, is a form of particulate matter and 
results from the incomplete combustion of coal, diesel fuel, and 
biofuels (such as alcohol or gasohol), and from open biomass burning, 
(i.e., the burning of forests and agricultural residues). Because it is 
dark in color, black carbon aerosol absorbs the sun's energy, creating 
warming in the atmosphere and cooling at the earth's surface, thus 
modifying climate (in contrast to the warming caused by traditional 
greenhouse gases, which prevent the earth's heat from escaping into 
space). Black carbon is generally released with other pollutants in 
different proportions.

* Tropospheric ozone is not emitted directly but is formed when 
emissions of other pollutants, called precursors, react in the presence 
of sunlight. Ozone precursors include nitrogen oxides (mainly nitric 
oxide and nitrogen dioxide) and several carbon-containing substances, 
namely carbon monoxide, methane, and non-methane volatile organic 
compounds. Nitrogen oxides are produced primarily by motor vehicles, 
other combustion engines, and electric power plants. Natural sources of 
nitrogen oxides are lightning and biological processes in soils. Carbon 
monoxide is formed when the carbon in fuels is not burned completely. 
It is a product of motor vehicle exhaust and industrial processes. 
Natural sources of carbon monoxide include wildfires. Methane is 
emitted by human activities, such as coal mining, natural gas and oil 
production, livestock production, rice cultivation, and waste disposal. 
It also comes from natural sources, including wetlands, and some 
animals, such as termites. Volatile organic compounds are produced by 
motor vehicles, industrial processes using solvents, and in some cases, 
by vegetation, including trees.[Footnote 6]

In reviewing the scientific information on these three substances, we 
concentrated on the material covered in the most recent systematic 
published review, the IPCC's Third Assessment Report, which represents 
the consensus of many climate scientists. [Footnote 7] We also included 
some more recently published material, notably the large-scale, multi-
participant study of aerosols over the Indian Ocean, known as the 
INDOEX study, which was conducted in 1999. We included these results 
because they come from a large, well-recognized, international program 
whose objectives overlap substantially with many of the subject areas 
of this report.

The seven countries we reviewed differ greatly in terms of their 
population, total area, and per capita income. For example, population 
ranged from around 60 million in the United Kingdom [Footnote 8] to 
nearly 1.3 billion in China; total area varied from just under 
245,000 square kilometers for the United Kingdom to 9.6 million square 
kilometers for the United States; per capita income ranged from $2,200 
in India to $36,300 in the United States. See table 1.

Table 1: Comparative Statistics of the Seven Countries Reviewed:

Country: Economically developed countries: United States; Estimated 
population (2002) (in millions): 281.0; Total area (square kilometers): 
9,629,091; Per capita income, 2001: $36,300.

Country: Economically developed countries: United Kingdom; Estimated 
population (2002) (in millions): 60.0; Total area (square kilometers): 
244,820; Per capita income, 2001: 24,700.

Country: Economically developed countries: Germany; Estimated 
population (2002) (in millions): 83.3; Total area (square kilometers): 
357,021; Per capita income, 2001: 26,200.

Country: Economically developed countries: Japan; Estimated population 
(2002) (in millions): 127.0; Total area (square kilometers): 377,835; 
Per capita income, 2001: 27,200.

Country: Economically developed countries: China; Estimated population 
(2002) (in millions): 1,284.3; Total area (square kilometers): 
9,596,960; Per capita income, 2001: 4,301.

Country: Economically developed countries: India; Estimated population 
(2002) (in millions): 1,045.8; Total area (square kilometers): 
3,287,590; Per capita income, 2001: 2,200.

Country: Economically developed countries: Mexico; Estimated 
population (2002) (in millions): 103.4; Total area (square kilometers): 
1,972,550; Per capita income, 2001: 9,000.

Source: GAO (table), Central Intelligence Agency's The World Fact Book, 
2002 (data).

Notes: Some figures have been rounded.

[End of table]

Estimated gross domestic product per capita is based on purchasing 
power parity rates. Purchasing power parity asserts that a unit of 
currency, such as a dollar, should be able to buy the same bundle of 
goods in all countries.

In the 1960s, scientists determined that emissions of sulfur dioxide 
from European power plants were causing the acidification of 
Scandinavian lakes. Recognizing that air pollution does not respect 
national boundaries, 34 countries, including Germany, the United 
Kingdom, and the United States, signed the Convention on Long-Range 
Transboundary Air Pollution (CLRTAP) in 1979. Under a subsequent 
protocol to this convention, the signatories agreed to reduce their 
emissions of sulfur dioxide. Later, they extended the convention to 
further reduce sulfur dioxide and to reduce ozone precursors and 
various other pollutants. [Footnote 9] There are now 49 parties to 
the convention.

In addition to commitments under this 1979 convention, several European 
countries, including Germany and the United Kingdom, are bound by 
European Union (EU) requirements to reduce emissions. For example, a 
1996 framework directive set broad goals for the consistent management 
of several air pollutants, including sulfur dioxide, nitrogen oxides, 
and ozone, in member nations. In 1999, a supplemental directive 
established a legally binding limit on concentrations of sulfur dioxide 
and nitrogen oxides, among other substances, to be achieved by all 
member countries by 2005. Another 1999 directive required EU countries 
to reduce the sulfur content of liquid fuel. (More information on the 
various directives can be found in apps. II, III, and IV.) Each EU 
member nation is required to transform the EU requirements into 
national legislation for domestic implementation. In general, the EU 
emission reduction targets are more stringent than the CLRTAP targets.

Scientists Agree on the Overall Direction of the Three Pollutants' 
Climate Impacts, but the Estimates of Impacts Contain Significant 
Uncertainties:

According to the most recent comprehensive review of scientific 
research on climate change, published in 2001, scientists generally 
agree that sulfate aerosols tend to cool the earth, while black carbon 
aerosols and ozone tend to warm it. However, the extent of these 
effects is uncertain. Research published since 2001 has not changed 
these overall conclusions, but it does suggest that the scientific 
community's understanding of these effects is incomplete and needs 
further exploration.

The extent of the heating and cooling effects of various substances, as 
compared to pre-industrial conditions, is typically expressed in watts 
per square meter, which is a measure of energy per unit area. Changes 
in the balance between incoming and outgoing solar energy in turn heat 
or cool the earth. Specifically, the earth receives 342 watts per 
square meter of incoming solar radiation annually at the top of the 
atmosphere and reflects about 30 percent back into space, resulting in 
a net input of 240 watts per square meter. If the climate were in 
balance, the same amount of energy that the earth received would be 
emitted back into space as infrared radiation. However, warming gases 
trap some of this outgoing radiation, thereby changing the balance 
between incoming and outgoing radiation. Water vapor is the most 
significant greenhouse gas; carbon dioxide is the second most 
significant. Additional carbon dioxide added to the atmosphere by human 
beings since the industrial era has contributed another 1.46 watts per 
square meter averaged over the earth's surface annually, thereby 
further warming the climate. Figure 2 shows how the average effects of 
the three pollutants we reviewed compare with the climate effects of 
carbon dioxide and other conventional greenhouse gases.

Figure 2: Direct Effects of Several Substances on Climate Change as 
Reported in the IPCC's Third Assessment Report, 2001:

[See PDF for image]

[A] Estimated uncertainties for these substances are plus or minus 10 
percent.

[B] Synthetic gases include hydrofluorocarbons, perfluorocarbons, and 
sulfur hexafluoride.

[C] Estimated uncertainty for ozone is plus or minus 43 percent.

[D] Please see notes below for a discussion of the uncertainty 
surrounding sulfate aerosol and black carbon.

Notes: According to the IPCC, the level of scientific understanding is 
low for sulfate aerosol and very low for black carbon aerosol. The 
uncertainty estimates in the report are a factor of 2 for each of these 
substances. (Factor of 2 means, for example, in the case of sulfate 
aerosol, the upper end of the range would be -0.2, which is half the 
estimate--the estimate of 0.4 divided by factor of 2--and the lower end 
of the range would be -0.8, which is twice the estimate--the estimate 
of 0.4 multiplied by factor of 2.) Note that these uncertainty 
estimates are not based in statistics, but rather on the range found in 
the recent literature.

[End of figure]

Positive values indicate a warming effect; negative values indicate a 
cooling effect. The values for black carbon include only the burning of 
fossil fuels, but not other sources, such as biomass burning, which is 
estimated to make a similar-sized contribution to warming. Combustion 
of these substances also emits organic carbon aerosols, which 
contribute an opposite (cooling) effect on climate. These are all 
direct effects. Indirect effects, such as those operating through 
clouds, could increase the impacts of both sulfates and black carbon. 
Note that these uncertainty estimates are not based on statistical 
analysis, but rather are subjective judgments based on ranges found in 
reported studies. In addition, the values for these estimates are 
described in the IPCC Third Assessment Report as having different 
levels of scientific understanding associated with them: tropospheric 
ozone--medium; sulfate--low; and fossil fuel black carbon--very low.

These three pollutants are relatively short-lived and are distributed 
only locally or regionally, in contrast to the traditional greenhouse 
gases, which persist for many years and are distributed worldwide. In 
comparison, the effects of the short-lived substances must be averaged 
over time and space.

Sulfate aerosols. According to the 2001 review, scientists generally 
agree that sulfate aerosols contribute to cooling the earth. The 
uncertainty regarding the climate effects of sulfate aerosols is 
significantly higher than for tropospheric ozone. Because these 
aerosols are light colored, they do not absorb sunlight. Consequently, 
their effect is purely cooling, because they reflect sunlight back into 
space and prevent it from reaching the earth's surface. This cooling 
phenomenon is referred to as a direct effect on the climate. The total 
amount of sulfate aerosols in the atmosphere is estimated to be about 
10 times larger than the total amount of black carbon aerosols 
discussed below.

Scientists have also identified indirect cooling effects of sulfate 
aerosols that result from their effect on clouds. Like some other 
aerosols, sulfates become the nuclei onto which water vapor condenses, 
forming cloud droplets. There, they produce clouds composed of larger 
number of smaller droplets, which result in two indirect effects on the 
earth's climate. First, smaller droplets tend not to coalesce as 
readily into raindrops. Therefore, clouds composed of smaller droplets 
are less likely to produce rainfall and will persist longer. Since 
clouds scatter solar energy back out to space, they redirect energy 
away from the earth, causing cooling. Second, since smaller cloud 
droplets scatter more sunlight per mass than larger cloud droplets, 
even more solar energy will be directed away from the earth. Because of 
both the lessened rainfall from affected clouds and the changes in 
local heating of the earth, with consequent reduction in evaporation, 
sulfate aerosols can reduce the amount and change the distribution of 
rainfall in affected areas.

Black carbon. According to the 2001 review, scientists generally agree 
that black carbon aerosols contribute to warming the atmosphere. As 
with sulfate aerosols, the uncertainty associated with black carbon 
aerosols' warming effect is high. Much of the uncertainty about black 
carbon aerosols' effects is due to questions about how these aerosols 
mix with other types of aerosols and cloud droplets. In addition, black 
carbon is released in association with other pollutants, such as 
organic carbon, which has a cooling effect on climate. The proportions 
of each can differ substantially among sources.

According to recently completed research on the effect of aerosols in 
the atmosphere above the Indian Ocean, [Footnote 10] large amounts of 
aerosols--including some black carbon--in the air masses coming off the 
Indian subcontinent lead to dramatic reductions in the amount of solar 
radiation reaching the ocean's surface and may be reducing 
precipitation over polluted areas. While these results appear to be 
significant for a particular geographic area and time period, they have 
yet to be translated into globally averaged contributions to warming 
the earth's surface. Nevertheless, they suggest that these aerosols may 
have a larger effect on warming than was previously recognized.

Tropospheric ozone. According to the 2001 review, most scientists agree 
that tropospheric ozone [Footnote 11] contributes to warming the earth. 
The level of uncertainty associated with this warming effect is lower 
than the level for sulfate aerosols and black carbon but is greater 
than for carbon dioxide and other well-mixed greenhouse gases. However, 
ozone is not uniformly distributed throughout the troposphere because 
it is produced in a very uneven pattern in polluted areas and has a 
shorter lifetime than most other greenhouse gases. As figure 2 shows, 
its estimated warming effect is about one-quarter of the warming effect 
of carbon dioxide.

The formation of ozone in the atmosphere is complex. Most tropospheric 
ozone is generated by gases, called ozone precursors, that are emitted 
by industry, automobiles, and some natural sources, such as lightning 
and soil. There are two main classes of ozone precursors: nitrogen 
oxides (made up of nitric oxide and nitrogen dioxide) and certain 
carbon-containing gases, such as carbon monoxide and volatile organic 
compounds, including methane. Recent research suggests that reducing 
methane could have a greater effect in reducing ozone than previously 
recognized. [Footnote 12],[Footnote 13] This discovery is significant, 
since methane, unlike the other ozone precursors, lasts in the 
atmosphere for as long as 10 years. (See fig. 1.):

The Three Pollutants Are Generally Declining in Economically Developed 
Countries, but Not in Developing Countries; All Seven Countries 
Are Acting to Reduce Emissions:

The seven countries we reviewed have all enacted legislation and 
implemented regulations to reduce emissions of sulfur dioxide [Footnote 
14] and black carbon, and concentrations of tropospheric 
ozone. [Footnote 15] For the most part, the levels of the three 
pollutants are declining in the four economically developed countries 
and, to a limited extent, in the three economically developing 
countries.

Our analysis of measures to control emissions and concentrations of 
these substances is organized by pollutant; for each pollutant, we 
begin with the economically developed countries and then turn to the 
developing countries. Within the first group, we first discuss the 
United States because we found the most complete information about it. 
We next discuss the United Kingdom, Germany, and Japan, in declining 
order of available information. For economically developing countries, 
for similar reasons, the order is China, India, and Mexico.

Sulfur Dioxide Emissions Declined in Nearly All Countries; All Seven 
Countries Are Taking Steps to Reduce Them:

Of the three substances we reviewed, sulfur dioxide was the most widely 
measured and regulated. Appendix II describes each country's regulatory 
approach to sulfur dioxide emissions in greater detail.

Developed Countries:

Sulfur dioxide emissions have declined and are expected to continue to 
decline in the United States, United Kingdom, Germany, and Japan 
through at least 2010, owing to a combination of explicit government 
policies designed to curb sulfur dioxide emissions, the development of 
cleaner power generation and transportation technologies, and a 
continuing transition in many countries away from high-sulfur coal to 
low-sulfur coal and natural gas. Figure 3 shows the decline in 
emissions for the United States, the United Kingdom, and Germany 
between 1980 and 1999 and for Japan between 1990 and 1999, the only 
years for which we found data for that country. As the figure shows, 
the greatest decline occurred in Germany. In most of these countries, 
emissions declined more steeply between 1990 and 1999 than between 1980 
and 1990. Figure 4 shows projected declines between 1990 and 2010 (1995 
and 2010 for Japan). As the figure indicates, the greatest relative 
decline is expected to occur in Germany.

Figure 3: Sulfur Dioxide Emissions in Four Developed Countries, 
1980-99:

[See PDF for image]

Notes: A metric tonne is equivalent to 1.102 short tons (or 2,204 
pounds). We were unable to locate data from Japan for 1980 through 
1989.

[End of figure]

Figure 4: Projected Sulfur Dioxide Emissions in Four Developed 
Countries, 1990-2010:

[See PDF for image]

Notes: Projections of U.S. sulfur dioxide emissions do not include 
recent or proposed EPA rulemakings that are likely to decrease sulfur 
dioxide emissions in the future. Values from 2000 to 2010 for the 
United States, the United Kingdom, and Germany are based on 2010 
projections.

[End of figure]

Both the United States and European countries have health-based 
standards designed to minimize damage to human health caused by sulfur 
dioxide emissions. They also have annual emissions limits to control 
acidification of the environment caused by these emissions. The United 
States set its limits based on an across-the-board, 50-percent 
reduction in sulfur dioxide emissions, relative to 1980, from power 
plants. In contrast, the European governments set their standards using 
the "critical loads" approach, taking into consideration the estimated 
potential impact of the emissions on the environment. That is, the 
Europeans estimate, using mathematical models, the maximum amount of 
damage that a particular ecosystem--such as forests, lakes, and 
streams--could sustain before long-term harmful effects occur. 
Standards aimed at reducing emissions to a level near the critical load 
goal are then negotiated among countries. This type of standard is 
often referred to as an effects-based standard. We were unable to find 
information on how Japan developed its sulfur dioxide 
emissions standards.

United States. U.S. emissions of sulfur dioxide decreased from 
23.5 million metric tonnes to 17.1 million metric tonnes between 1980 
and 1999, a decrease of about 27 percent, according to U.S. data 
submitted to the CLRTAP. The United States projects that sulfur dioxide 
emissions will decline even further, to 15.1 million metric tonnes in 
2010, representing about a 36-percent decrease from 1980 levels (See 
fig. 4.) The decline in emissions in 2010 may be even greater because 
U.S. projections take into account only national policies but not state 
regulations. They also do not include proposed new measures.

Sulfur dioxide emissions started to decline in the United States in the 
early 1970s, after peaking at about 31 million tons. Federal regulation 
of sulfur dioxide emissions essentially began with the Clean Air Act of 
1970, as amended in 1977 and 1990. The act required the Environmental 
Protection Agency (EPA) to develop national air quality standards for 
air pollutants that may endanger public health and welfare. EPA 
established such standards for sulfur dioxide and several other 
pollutants. The act also required each state to develop a plan (to be 
approved by EPA) for meeting those standards. Under the act, all new or 
modified large power plants could emit no more than a specified rate of 
sulfur dioxide per unit of fuel consumed. Most new plants responded to 
this requirement by shifting to coals with lower sulfur content.

Concern about sulfur dioxide emissions increased again in the late 
1970s and early 1980s, when scientists noticed that lakes and streams, 
particularly in the Northeast, were becoming increasingly acidic, 
thereby threatening aquatic life. This acidity was traced to sulfur 
dioxide and nitrogen oxide emissions from power plants, primarily those 
located upwind in the Midwest. The 1990 Clean Air Act Amendments 
imposed additional controls on such emissions. One of the programs 
created under the amendments was the Acid Rain Program, which employs 
emissions trading, a market-based mechanism, to reduce sulfur dioxide 
emissions.

United Kingdom. According to data submitted to the CLRTAP, the United 
Kingdom reduced its sulfur dioxide emissions from just under 
4.9 million metric tonnes in 1980 to about 1.2 million metric tonnes in 
1999, a decrease of about 75 percent. The majority of the reduction was 
due to an increase in the use of nuclear and renewable energy, fuel-
switching (e.g., to natural gas), improvements in efficiency, flue gas 
desulfurization, [Footnote 16] and fuel sulfur reductions. The United 
Kingdom projects that its sulfur dioxide emissions will decline even 
further, from about 1.2 million metric tonnes in 1999 to 0.6 million 
metric tonnes in 2010, an additional decrease of nearly 50 percent. If 
realized, this decrease would represent an 87-percent reduction from 
the 1980 level.

Sulfur dioxide emissions, along with other pollutants, contributed to 
several major smog episodes in London during the first 6 decades of the 
20th century, with the most significant one occurring in December 1952. 
That episode took more than 4,000 lives over 5 days. It also led to the 
enactment of legislation in 1956 and 1968 that aimed to reduce 
emissions from households. A 1990 law gave the government the power to 
set emissions limits and environmental quality standards for industrial 
plants. A 1995 law introduced a new framework for air quality policy, 
giving added prominence to the concept of air quality standards.

In addition, the United Kingdom has international obligations to reduce 
sulfur dioxide emissions. As a party to the CLRTAP, the United Kingdom 
intends to reduce its annual emissions of sulfur dioxide by at least 
80 percent by 2010 from its 1980 level. Furthermore, it must comply 
with EU requirements to reduce sulfur dioxide emissions. (See 
app. II.):

Germany. According to data submitted under the CLRTAP, sulfur dioxide 
emissions in the unified Germany declined by nearly 85 percent, from 
5.3 million metric tonnes to 0.83 million metric tonnes between 1990 
and 1999. This decline resulted from such factors as the post-1990 
economic restructuring, the retirement of outdated plants in the former 
East Germany, and the use of less sulfur-intensive fuels. Germany 
reports that it expects to reduce its sulfur dioxide emissions by about 
34 percent between 1999 and 2010.

West Germany began to regulate sulfur dioxide in the late 1970s, when 
it signed the CLRTAP. It participated in this effort in part out of 
concern that sulfur dioxide-induced acidification was killing large 
numbers of trees in the forests of southwestern Germany.

West Germany's emissions of sulfur dioxide declined markedly during 
the 1980s, mainly because utilities expanded their use of natural gas 
to generate electricity, installed flue gas desulfurization technology 
in power plants, and substituted less sulfur-intensive fuels at power 
plants and in industry. In contrast, emissions in the former East 
Germany rose until 1987, mainly because utilities there used lignite 
(low-grade coal) to generate electricity.

Germany's primary legislative instrument to control sulfur dioxide and 
other air emissions is a 1974 law, amended in 2000, that regulates 
emissions from both large and small combustion facilities. Supporting 
ordinances contain detailed regulations and emissions limits for all 
facilities covered by the act. Germany is also reducing its sulfur 
dioxide emissions under both the CLRTAP and EU directives.

Japan. According to the Japanese government, sulfur dioxide emissions 
declined by about 9 percent between 1990 and 1999, or from 0.97 million 
metric tonnes to 0.87 million metric tonnes. According to another 
source--a researcher from the Japanese government's National Institute 
for Environmental Studies--sulfur dioxide emissions may decline by 
27 percent between 1995 and 2010.[Footnote 17]

Compared with other industrialized countries, particularly the United 
States and Germany, Japan uses considerably less coal, relying instead 
on nuclear power to generate one-third of its electricity. 
Nevertheless, in 1968, Japan began to regulate sulfur dioxide and other 
substances created by fuel combustion. It set standards for emissions 
from power plants and factories and provided for stations in several 
parts of the country to monitor emissions of sulfur dioxide and other 
substances. In the late 1970s, the government required facilities to 
install scrubbers in their smokestacks. Japan also reduced its sulfur 
dioxide emissions through gains in combustion efficiency and a 
transition to low-sulfur coal.

Developing Countries:

As in the developed countries, China and Mexico saw an overall decrease 
in sulfur dioxide emissions during the 1990s, as shown in figure 5. We 
were unable to find data for India. Sulfur dioxide emissions in China 
declined by 15 percent between 1997 and 2000, in part as a result of 
the combination of emission reduction policies and a decline in coal 
use. However, emissions increased slightly after 1999. According to 
Mexico's National Greenhouse Gas Inventory, sulfur dioxide emissions 
decreased by about 55 percent between 1990 and 1998, though they 
increased very slightly between 1993 and 1998. We were unable to find 
consistent historical data on sulfur dioxide emissions in India. We 
were also unable to find data on projected emissions levels for any of 
these three countries. According to U.S. experts, the quality of some 
of the data for these countries is uncertain, due in part to old 
measuring equipment and techniques.

Figure 5: Sulfur Dioxide Emissions in China and Mexico, Selected Years:

[See PDF for image]

[End of figure]

China. China is currently the world's largest emitter of sulfur 
dioxide. It relies heavily on coal as an energy source, and the 
country's sulfur dioxide emissions rose initially along with rapid 
industrialization. More recently, according to the Chinese State 
Environmental Protection Administration, emissions of sulfur dioxide 
declined from 23.4 million metric tonnes to 20 million metric tonnes 
between 1997 and 2000.

Although under its current 5-year plan (2001-2005), China aims to 
reduce coal consumption by increasing the share of natural gas and 
renewable energy in the total energy supply, the U.S. Department of 
Energy's Energy Information Administration (EIA) projects that coal 
combustion in China will increase 60 to 194 percent between 1999 and 
2020, depending on assumptions about economic growth. Thus, sulfur 
dioxide emissions could also rise, unless implementation of a 1987 Air 
Pollution Control Law, amended in 2001, can slow or reverse this trend. 
The law is designed to improve air quality in large-and medium-sized 
cities through stiffer penalties, better enforcement, and greater use 
of market-based methods, such as the imposition of sulfur dioxide 
discharge fees. It also provides incentives for using high quality, low 
sulfur coal and requires new or expanded sulfur dioxide-emitting power 
plants and large-and medium-sized enterprises to install sulfur dioxide 
scrubbing equipment.

India. We found limited data on India's sulfur dioxide emissions. 
Specifically, we found estimates from one source for 1980 and 1990, 
which showed an 82-percent increase. We found an estimate from another 
source for 2000 alone, which is higher than the 1990 estimate from the 
other source. However, because these sources used different estimating 
methods, their results may not be comparable.

We were also unable to find sulfur dioxide projections for India. 
However, the EIA projects that India's coal consumption will increase 9 
to 62 percent between 1999 and 2020, depending on assumptions about 
economic growth. It also notes that, because of shortages in generating 
capacity and public funds, India will probably continue to rely on old, 
coal-fired plants for some time, despite their contribution to the 
country's air quality problems.

Coal accounts for more than half of India's primary fuel consumption, 
but the sulfur content of the coal used is relatively low. 
Nevertheless, India has undertaken some steps to reduce sulfur dioxide 
emissions from coal. For example, it has improved the combustion 
efficiency of conventional coal technologies and has promoted the use 
of renewable energy technologies as an alternative to coal. It further 
adopted national air quality standards for sulfur dioxide and other 
pollutants in 1982 and revised them in 1994. India has also reduced the 
sulfur content of oil products. According to the EIA, India's high 
levels of pollution do not result from a lack of effort in building a 
sound system of legislation and regulation, but rather from weak 
enforcement at the local level.

Mexico. According to the Mexican government, sulfur dioxide emissions 
decreased by 67 percent between 1990 and 1992, but started to increase 
gradually after 1992. Between 1990 and 1998, however, the net decrease 
was 55 percent. We were unable to find data on projected sulfur dioxide 
trends. However, Mexico has considerably expanded its use of natural 
gas, which produces less sulfur than coal, and according to a 2002 
report by the EIA, most new power plants in Mexico are likely to be 
gas-fired, although some new coal-fired plants will also be 
constructed. EIA projects that coal consumption will grow 62 to 115 
percent between 1999 and 2020, depending on assumptions about economic 
growth. Most of Mexico's energy comes from oil, with coal providing 
only about 4 percent of the country's energy requirements.

The basic law for reducing air pollution emissions is the 1988 General 
Law of Ecological Equilibrium and the Protection of the Environment. 
The law provides the framework for air pollution standards for all 
major substances. Environmental protection became a particularly 
important issue for Mexico in the early 1990s as a result of 
negotiations for the North American Free Trade Agreement with the 
United States and Canada. In 1992, the Mexican government created a 
special office to enforce regulations. This office is charged with 
inspecting facilities and issuing penalties for noncompliance. 
According to Mexican government officials, Mexico's limited financial 
resources prevent full enforcement of environmental regulations, 
despite steadily improving enforcement efforts. Mexico has also 
introduced a federal tax incentive program for purchasers of pollution 
control equipment. In addition to national legislation, some air 
quality initiatives are underway in large cities, where urban air 
pollution is a significant problem.

Black Carbon Emissions Generally Declined in Developed Countries and 
Generally Increased in Developing Countries:

Scientists have begun to recognize the importance of black carbon as an 
agent of climate change only within the past few years. Consequently, 
most countries do not directly track emissions of this pollutant. 
Therefore, to conduct our analysis, we used a global black carbon 
database developed by atmospheric researchers. [Footnote 18] This 
database has several limitations. First, as with most emissions 
inventories, estimates in this database are not based on actual black 
carbon measurements, but rather are calculated using information on 
countries' use of fossil fuel, which is measured, along with estimates 
of how the fuel is used. Second, this database does not contain 
historical information on open biomass burning (forest burning or land-
clearing), which may account for as much as 50 percent of black carbon 
emissions. Finally, emissions estimates are based on limited 
information about the characteristics of the fuels and technologies 
that produce the emissions.

Black carbon emissions are particularly difficult to track because they 
are often produced by activities that are informal and unregulated, 
and in developing countries, there is considerable consumption of 
noncommercial fuels, such as wood or animal waste. Since these fuels 
are not reported the same way as fossil fuels, neither the amounts used 
nor the emissions produced are well quantified. Because sophisticated 
emission measurements have usually been available only in developed 
countries, moreover, there are few measurements of the combustion that 
produces most black carbon emissions in developing countries. For these 
and other reasons, the black carbon emissions data are highly 
uncertain. Despite these weaknesses, this database is currently the 
only source we found that contained consistently estimated information 
on different countries' emissions.

Black carbon usually comes from the same sources as organic carbon, 
which has a cooling effect on climate. It would be difficult to control 
emissions of either substance separately; hence, it would therefore be 
difficult to control warming by reducing black carbon emissions. 
Although countries do not regulate black carbon directly, it is one 
component of what regulatory agencies often refer to as particulate 
matter, [Footnote 19] and most of the countries we reviewed do regulate 
particulate matter. We therefore collected information on measures to 
reduce particulate matter, recognizing that this pollutant is an 
imperfect proxy for black carbon. Furthermore, even when particulate 
matter emissions are reduced, black carbon levels may not decline 
because some types of particulate matter, such as sulfate, do not 
contain black carbon when emitted.

Developed Countries:

According to the database we used, the majority of black carbon 
emissions in developed countries results from the combustion of diesel 
fuel by vehicles, including both on-road vehicles, such as heavy-duty 
trucks, and off-road vehicles, including farm and construction 
equipment. As figure 6 shows, black carbon emissions from fossil fuel 
combustion declined in three of the four developed countries, more in 
the United Kingdom and Germany and less in the United States. During 
this period they increased in Japan, starting in the early 1980s. (See 
app. III for more detail on policy measures to reduce black 
carbon emissions.):

Figure 6: Black Carbon Emissions in the United States, United Kingdom, 
Germany, and Japan, 1980-96:

[See PDF for image]

Note: Graphic based on global black carbon database prepared by T.C. 
Bond and D.G. Streets for an article entitled, "A Technology-Based 
Global Inventory of Black and Organic Carbon Emissions from 
Combustion," to be submitted to the Journal of Geophysical Research.

[End of figure]

United States. According to the database we examined, black carbon 
emissions in the United States were approximately 4 percent lower in 
1996 than in 1980. However, there was a steady increase from 1992 to 
1996. According to this database, about one-half of black carbon 
emissions in the United States are from the use of diesel vehicles to 
transport goods over long distances and from off-road diesel vehicles. 
However, the database may not fully reflect the effects of certain 
technologies that were introduced in the 1990s to reduce diesel 
emissions. Including such technologies in the database would likely 
show greater emissions declines during the 1990s. Gasoline-fueled cars 
and wood combustion in home fireplaces and stoves are other, smaller 
sources of black carbon emissions.

The United States is the only country for which we found projections of 
black carbon emissions. These were developed in support of an EPA 
rulemaking [Footnote 20] relating to large trucks. When the rule is 
fully implemented in 2030, black carbon emissions are expected to 
decrease by an estimated 109,000 tons from the level produced in 
1996.[Footnote 21]

The United States has several efforts underway to help reduce emissions 
of black carbon and other types of particulate matter. Under the Clean 
Air Act, EPA promulgated national air quality standards for particulate 
matter in 1971 and has regulated particulate matter emissions from 
highway motor vehicle engines. The most recent rule is designed to 
reduce emissions from heavy-duty diesel vehicles by improving diesel 
engines and reducing the sulfur content of diesel fuel. [Footnote 22]

United Kingdom. According to the database we used, black carbon 
emissions from the United Kingdom declined by about one-third between 
1980 and 1996. The sources of black carbon emissions in the United 
Kingdom are similar to those in the United States, with the majority of 
emissions produced by diesel vehicles. Other sources of black carbon 
emissions are industrial coke-making [Footnote 23]and coal-burning in 
the residential sector, although residential coal use is declining in 
the United Kingdom.

The Parliament enacted legislation in 1956 and 1968 to control domestic 
sources of particulate matter. The 1956 act aimed to control domestic 
sources of smoke pollution by introducing smokeless zones (regions 
where smokeless fuel had to be burned) and by making grants to 
homeowners to convert their homes from traditional coal fires to 
heaters fueled by oil, gas, smokeless coal, or electricity. Legislation 
in 1990 and 1995 brought many smaller emission sources under air 
pollution control by local authorities for the first time. These acts 
also provided a new statutory framework for local air quality 
management. In 1997 the United Kingdom published its first national air 
quality strategy, which set air quality standards and objectives for 
the pollutants of greatest concern, including particulate matter. The 
United Kingdom changed the particulate objective under this strategy in 
2000, in response to a new EU directive and then in 2002 strengthened 
the objective once more.

In the transportation sector, the EU in 1992 introduced directives 
containing exhaust emission limits (generally referred to as the Euro I 
standards) for new medium-and heavy-duty diesel engines. The standards 
aimed to reduce emissions of particulate matter, as well as carbon 
monoxide, hydrocarbons (including volatile organic compounds), and 
nitrogen oxides, all ozone precursors. More stringent emission limits 
for these vehicles, called Euro II, came into effect in 1996. Euro III 
limits were adopted in 1999, and even more rigorous standards for these 
vehicles, Euro IV and Euro V, are expected to take effect in 2005 and 
2008, respectively. The EU also set standards in 2001 for maximum 
allowable levels on the sulfur content of diesel fuel. The directive, 
effective January 1, 2005, will introduce sulfur-free diesel and 
gasoline in all EU member states.

Germany. Black carbon emissions in Germany also declined by about 
one-third between 1980 and 1996, according to the Bond and Streets 
database. While diesel consumption and emissions increased rapidly 
during this time, a phase-out of coal combustion for home heating led 
to an overall reduction in black carbon emissions. Other large sources 
of black carbon emissions in Germany--much smaller than diesel 
vehicles--are industrial coking coal and gasoline vehicles.

Between 1990 and 1996, Germany decreased its emissions of particulate 
matter by 86 percent. The decrease occurred primarily because of 
developments in eastern Germany after reunification, when many older 
industrial and power plants were closed or refitted with new 
technologies that remove soot particles. In addition, many 
installations shifted to the use of gas and liquid fuels--especially in 
small combustion appliances--thereby producing less particulate 
matter. The Federal Emission Control Act provides the framework for 
regulating all air pollutants, and its ordinances govern both large and 
small combustion facilities.

Like the United Kingdom, Germany must abide by EU directives aimed at 
reducing particulate matter emissions, including the Euro I-III 
directives on diesel vehicle emissions. Most diesel vehicles currently 
emit much less particulate matter than earlier models, but Germany is 
continuing its effort to reduce emissions in the transportation sector. 
For example, in 2001 Germany passed legislation to offer tax breaks for 
sulfur-free gasoline and diesel fuel starting this year.

Japan. Black carbon emissions in Japan were about 60 percent higher in 
1996 than in 1980, according to the database we used. The major source 
of these emissions is diesel fuel, the use of which began to increase 
in 1988. As in the United Kingdom and Germany, coke-making could be an 
additional source of black carbon emissions in Japan.

In June 2001, Japan's legislature enacted a law to further tighten 
particulate matter emissions from diesel-powered vehicles to improve 
air quality in major urban areas. The law applies to 196 local 
governments in Tokyo, Osaka, and four other cities.

Developing Countries:

The database we used indicates that black carbon emissions increased 
between 1980 and 1996 in China and India, as figure 7 shows. It 
suggests that Mexico's black carbon emissions are essentially unchanged 
over this period. We found no projections of black carbon for any of 
these three developing countries.

Figure 7: Black Carbon Emissions in China, India, and Mexico, 1980-96:

[See PDF for image]

Note: Graphic based on global black carbon database prepared by T.C. 
Bond and D.G. Streets for an article entitled, "A Technology-Based 
Global Inventory of Black and Organic Carbon Emissions from 
Combustion," to be submitted to the Journal of Geophysical Research.

[End of figure]

China. Emissions of black carbon in China rose by 43 percent between 
1980 and 1996, according to the Bond and Streets database. Moreover, 
according to that data source, China emits more black carbon than any 
other nation in the world--approximately 29 percent of the global 
total. However, its per capita emissions are not higher than those of 
other countries. These emissions came primarily from coal (especially 
dirty soft coal) and wood in the residential sector, coal-burning power 
plants using older technologies, on-road and off-road diesel vehicles, 
and coke-making plants in the industrial sector. Emissions increased 
steeply in the 1980s, but the growth rate slowed somewhat in the 1990s 
as China began to switch from coal to cleaner natural gas and from raw 
coal to coal briquettes (which produce fewer emissions) in the 
residential sector; it also closed many small industrial coal plants.

Under amendments in 2000 to its Air Pollution Control Law, the 
government set a goal of reducing "soot and flue dust" (particulate 
matter) emissions to 1995 levels by 2010. According to the law, new or 
expanded power plants and large-and medium-sized industrial facilities 
must install particulate matter control equipment or take other 
measures to reduce emissions. The city of Beijing requires the use of 
gas in place of coal in new fuel applications.

In the transportation sector, China has implemented emissions standards 
for diesel vehicles. In 2000 and 2001 the government introduced the 
Euro I emissions standards for new cars and trucks. The standards, 
which apply to the entire country, are based on those standards 
originally introduced in Europe in 1992 and limit the amount the amount 
of particulate matter and other substances that can be emitted from new 
diesel vehicles. More stringent Euro II norms currently apply to 
Beijing and Shanghai and will apply to the entire country after 2005.

India. According to the database we used, black carbon emissions in 
India rose by just under one-third between 1980 and 1996. Most of this 
country's emissions come from the use of biofuel in the residential 
sector, with diesel vehicles contributing a smaller, but noticeable, 
fraction. Black carbon emissions increased between 1980 and 1996, as 
the population grew and burned more wood, dung, and agricultural waste 
for cooking and home heating. [Footnote 24] The Environmental Protection 
Act of 1982 set national standards for the emissions of various 
substances. The standards were revised in 1994. Revisions to the act in 
1996 set fuel quality specifications, including requirements for low-
sulfur diesel. In the capital city of New Delhi, 84,000 public vehicles 
were converted from gasoline and diesel to compressed natural gas, 
which emits negligible particulate matter. In 2000, the Indian 
government introduced Euro I standards for private, non-commercial 
vehicles throughout the country. Euro II norms currently apply to 
New Delhi and will apply to the entire country after 2010.

Mexico. Black carbon emissions in Mexico remained fairly constant 
between 1980 and 1996, according to the database we used. Mexico is not 
a large consumer of coal, instead relying primarily on oil as its key 
energy source. Most of its black carbon emissions come from diesel fuel 
use. However, according to a Mexican government official, in rural 
areas, villagers burn propane or biomass for home cooking; biomass 
produces black carbon emissions. Older gasoline cars also produce black 
carbon emissions in Mexico.

Trends in Surface Ozone Concentrations Are Mixed, but Background Ozone 
Levels in the Troposphere Appear to Be Rising, With Implications for 
both Air Quality and Climate:

The earth's weather takes place in the lowest layer of the atmosphere, 
called the troposphere, which extends from the earth's surface to 
between 9,000 and 16,000 meters above the surface. Within the 
troposphere, ozone concentrations differ between zones, [Footnote 25] 
the boundary layer, which extends from the earth's surface to roughly 
500 to 3,000 meters above the earth's surface, and the much larger free 
troposphere. (The height of the boundary layer can vary by time of day 
and season: higher in the daytime and in summer, and lower in winter 
and at night.) Ozone in these two zones has different durations and 
effects. There are important interactions between the two zones.

Ozone in the boundary layer generally results from human activity, such 
as transportation and fossil fuel combustion. Peak ozone episodes 
usually occur in the summer months, under conditions of long periods of 
bright sunshine, warm temperatures, light winds, and abundant ozone 
precursors. Changing weather patterns contribute to yearly differences 
in ozone concentrations from region to region.

Boundary layer ozone lasts only a few days over land, where it gets 
deposited on surfaces. Over large bodies of water, such as oceans, it 
can last longer, since there are no surfaces for deposition. At high 
concentrations ozone can contribute to human respiratory problems and 
plant damage.

The free troposphere is much larger than the boundary layer and extends 
several miles above the boundary layer to the top of the troposphere. 
Ozone in the free troposphere consists of some naturally occurring 
ozone (such as ozone produced by lightning and ozone descending from 
the stratosphere), as well as human-generated ozone carried upward from 
the boundary layer by wind. Ozone in the free troposphere generally 
lasts longer than ozone in the boundary layer--from 1 to several 
weeks. [Footnote 26] In the free troposphere, ozone, like other 
greenhouse gases, can trap surface radiation and contribute to warming 
the earth.

Air is exchanged extensively between the boundary layer and the free 
troposphere. Consequently, ozone pollution arising from the boundary 
layer--particularly in the northern hemisphere--has contributed to 
increased levels of ozone in the free troposphere. Hence, the 
troposphere--the source of clean air at the earth's surface--is showing 
an increasing background level of ozone. [Footnote 27] With the higher 
concentrations of ozone in the free troposphere and in remote regions, 
more ozone can be blown into populated areas, worsening the local 
pollution. Ozone pollution has also been carried to the surface over 
remote regions, such as the oceans and the Arctic.

Current estimates of ozone concentrations are based on profiles from 
ozone balloons equipped with measuring devices (sondes). However, these 
sondes are released from locations that are sparsely distributed around 
the globe. Because the information from the sondes is so limited, we 
used two types of proxy data to illustrate trends in the free 
troposphere, where ozone can affect the climate. First, we used 
historical data on ozone at the surface, which regulatory agencies, 
such as EPA, gather for air quality purposes. These data are measured 
at a network of monitoring stations, mainly in developed countries, and 
are collected primarily from urban and suburban areas, where ozone is a 
major health concern. Second, we used the results of a global modeling 
study that depicts ozone concentrations in the free troposphere.

Some developed countries have prepared projections of ozone 
concentrations at the surface, but because ozone projections prepared 
for air quality purposes do not adequately represent ozone increases in 
the free troposphere, where it is important for climate, we also used 
the results of a modeling study from the Harvard University Atmospheric 
Chemistry Modeling Group. [Footnote 28] These model results are based on 
an IPCC scenario that assumes that in 2025 there will be high 
population growth; significant income disparities between developed and 
developing countries; continued dominance of fossil fuels, including 
coal, in developing countries; and some policy measures in place to 
control ozone precursors. We used these results to represent annually 
averaged ozone concentrations in the free troposphere over the entire 
globe in 1990 and 2025. Unlike regional-scale air quality models, such 
as those used by regulatory agencies, the Harvard model is able to 
project ozone concentrations in the free troposphere and at a global 
level, which is of greatest interest for climate change purposes.

Figure 8 shows calculated ozone concentrations at 5 kilometers 
(about 3 miles) above sea level for 1990, while figure 9 shows 
projected concentrations in 2025. Both maps are based on the Harvard 
model. A comparison of the two maps indicates that free tropospheric 
ozone levels are expected to increase over the next two decades. 
Increased emissions of ozone precursors in Asia lead to higher ozone 
concentrations aloft, with possible consequences for climate 
change. [Footnote 29]

The most significant of the precursors in this scenario is likely to be 
methane, [Footnote 30] also a greenhouse gas, which is projected in the 
scenario to increase globally by about 20 percent from its present 
level. Thus, methane poses two problems: it can contribute directly to 
climate change as a greenhouse gas, and it can indirectly contribute to 
climate change as an ozone precursor.

Figure 8: Annually Averaged Global Ozone Concentrations at 
5 Kilometers, Parts per Billion, 1990:

[See PDF for image]

[End of figure]

Figure 9: Projected Annually Averaged Global Ozone Concentrations at 
5 Kilometers, Parts per Billion, 2025:

[See PDF for image]

[End of figure]

Developed Countries:

Approaches to boundary layer ozone regulation in the United States 
and Europe differ. The U.S. approach is almost exclusively health-
based. That is, its standards are designed to decrease prolonged human 
exposures to ozone. By contrast, the European approach, as with sulfur 
dioxide regulation, considers the cumulative effect of ozone 
concentrations on human health and the environment. It seeks to reduce 
these concentrations below those levels that affect public health and 
that can cause long-term damage to the environment. Since the 
environment can be impaired at lower concentrations than can human 
health, ozone concentrations associated with European goals are lower 
than in the United States. While the United States has firm air quality 
standards for ozone, the EU has non-mandatory target values for ozone 
concentrations but mandatory emission ceilings for ozone precursors, 
arrived at after a process that takes both local ozone formation and 
transboundary transport into consideration. Neither the United States 
nor most European countries consistently meet their ozone standards in 
polluted areas. We were unable to find information on how Japan sets 
its ozone standard.

Cumulative ozone levels in the boundary layer have generally risen over 
the past century--particularly because of ozone produced in the 
northern hemisphere. However, some developed countries, such as the 
United States, the United Kingdom, and Germany, have reported fewer 
exceedances of their ozone standards over the past decade. That is, 
peak ozone episodes, in which boundary layer ozone concentrations rise 
substantially above naturally occurring levels, are becoming somewhat 
less frequent and extreme in many developed countries. The governments 
attribute the improvement principally to policy measures over the past 
decade or so. However, weather conditions and other factors can affect 
year-to-year changes. Figure 10 shows that the number of locations 
exceeding their respective ozone standards declined by nearly 
70 percent in the United States and by nearly 90 percent in Germany 
between 1990 and 2000. We were unable to find comparable data for the 
United Kingdom and Japan. (More detailed information on ozone policies 
can be found in app. IV.):

Figure 10: Number of Areas Exceeding the Ozone Standard, United States 
and Germany, 1990-2000:

[See PDF for image]

Note: The U.S. ozone standard trend depicted here is 0.12 parts per 
million averaged over 1 hour. The U.S. also has an 8-hour ozone 
standard. The German ozone standard tracked here is 0.055 parts per 
million averaged over 8 hours.

[End of figure]

United States. Under the Clean Air Act of 1970, EPA was charged with 
developing air quality standards for air pollutants that may endanger 
public health and welfare. EPA established such standards for ozone and 
nitrogen oxides, an ozone precursor, in 1971. In 1979 EPA revised the 
ozone standard to 0.12 parts per million daily maximum over a 1-hour 
period that is not to be exceeded more than once per year on average. 
In 1997 EPA tightened the standard to 0.08 parts per million averaged 
over 8 hours. Although EPA has not yet begun to enforce the new 8-hour 
standard, it does track concentrations in terms of this standard. 
According to EPA, national ozone levels decreased 21 percent based on 
the 1-hour standard and 10 percent based on the 8-hour standard between 
1981 and 2000. For 52 metropolitan areas, the trend for 1-hour ozone 
levels improved between 1981 and 2000. However, beginning in 1994, the 
rate of improvement started to level off, and the trend since then has 
been relatively flat.

The U.S. effort to control ozone has focused mainly on reducing 
emissions of nitrogen oxides and volatile organic compounds, the two 
classes of ozone precursors. The Clean Air Act requires each state with 
ozone concentrations above the standard to develop a plan-known as a 
state implementation plan--for reducing ozone formation; EPA must 
approve this plan. This reduction can be attained through a mix of 
regulations in various sectors, such as the utility, transportation, 
and industry sectors--where most emissions occur. The ozone precursor 
methane is also controlled under Clean Air Act regulations that require 
the combustion of certain landfill gases from large landfills.

United Kingdom. According to United Kingdom government data, peak ozone 
concentrations declined by 30 percent during the 1990s. Emissions of 
nitrogen oxides declined by 42 percent between 1990 and 1999, while 
emissions of volatile organic compounds, another ozone precursor, 
declined by 34 percent between 1988 and 1999. The reductions in 
precursor emissions are mainly due to stricter regulations, an 
increasing share of vehicles fitted with catalytic converters (to 
control nitrogen oxides, volatile organic compounds, and carbon 
monoxide), and reduced nitrogen oxide emissions from power plants.

Incorporated into the United Kingdom's framework for improving air 
quality are several measures to address ozone formation. Many of these 
measures were developed within the framework of the CLRTAP or the EU. 
For example, in the transportation sector, implementation of the EU's 
Euro I standards limited emissions of the ozone precursors carbon 
monoxide, hydrocarbons (including volatile organic compounds), and 
nitrogen oxides from gasoline vehicles. More stringent standards came 
into effect in 1997 and 1998, depending on vehicle type, and are known 
as Euro II. These were superceded by Euro III standards for the 
majority of vehicles in January 2001. A further tightening of the 
emissions limits, referred to as Euro IV, will begin in January 2005 
and will be fully in force by January 2007.

Certain convention protocols also limit emissions of nitrogen oxides 
and volatile organic compounds. The United Kingdom also has a domestic 
target for ozone, which is more stringent than that of the EU.

Germany. According to the German government, peak ozone concentrations 
have been declining since the mid-1990s. Between 1990 and 2000, 
emissions of nitrogen oxides declined by 40 percent, and emissions of 
volatile organic compounds fell by 49 percent. The reductions were due 
both to regulations--mainly in the transportation sector--and to 
economic restructuring in the new states of eastern Germany.

Germany, like most other EU countries, has several measures in place 
for reducing nitrogen oxides and volatile organic compounds, both ozone 
precursors. These include emission-based motor vehicle taxes on heavy 
utility vehicles and automobiles and requirements to install advanced 
emissions reducing devices (that is, catalytic converters) on vehicles. 
Measures in the utility and industry sectors will also increase the 
efficiency of fuel combustion to reduce emissions of nitrogen oxides. 
Germany is bound by the same EU directives and CLRTAP protocols as the 
United Kingdom.

Japan. According to the Organization for Economic Cooperation and 
Development, ozone concentrations have increased in urban areas by 
about 5 percent since the late 1980s. However, according to Japanese 
data submitted under the United Nations Framework Convention on Climate 
Change, nitrogen oxide emissions increased by nearly 7 percent between 
1990 and 1999, while emissions of volatile organic compounds decreased 
by just over 3 percent.

In addition to its basic air quality framework, discussed earlier, 
Japan has several laws targeted at reducing ozone precursors. The 1968 
Air Pollution Control Law established standards for photochemical 
oxidants (ozone) and other substances, including the ozone precursors 
nitrogen dioxide and carbon monoxide. In 1992 the government introduced 
the Automobile Nitrogen Oxides Law to tighten controls on nitrogen 
oxide emissions from vehicles in areas where improvements in emissions 
were difficult to realize with existing measures. Among other things, 
the law regulates the types of vehicles that can be driven in areas 
where nitrogen oxide emissions exceed the environmental standard. The 
Japanese government has also set emission standards for nitrogen oxides 
for each industrial facility. The standards vary according to boiler 
type. Additionally, Japan's air pollution control law regulates 
volatile organic compound emissions from motor vehicles.

Developing Countries:

According to the World Health Organization, some of the poorest air 
quality in the world, due in part to ozone pollution, is found in 
Beijing, China; New Delhi, India; and Mexico City, Mexico. However, we 
were unable to find national data on ozone concentrations for these 
three countries. China and Mexico monitor ozone only in selected large 
metropolitan areas. In Mexico City, ozone levels have declined 
slightly since the early 1990s. We found no information on India. The 
IPCC reported that emissions of nitrogen oxides--an ozone precursor--in 
East Asia are increasing by about 4 percent per year. This suggests 
that ozone levels may rise along with continuing industrialization in 
that region.

China. Vehicle emissions are one of the major sources of air pollution 
in China's major cities. The country currently has over 40 million 
vehicles, and the number is growing by 10 percent annually; in large 
cities the rate of growth is even higher. The Euro I vehicle emissions 
standards in place around the country limit levels of carbon monoxide, 
hydrocarbons, and nitrogen oxides. The Euro II standards, in place in 
Beijing, aim to further reduce vehicle emissions in that metropolitan 
area.

Mexico. Efforts are underway to reduce emissions in the transportation 
sector, particularly in Mexico City. Since 1993, the Mexican government 
has increased its efforts to inspect motor vehicles. As of 2001, 230 
new car models had undergone emissions inspections. Another program 
reduces the number of cars on the road in Mexico City and provides 
incentives for the purchase of cars with lower emissions.

India. As in China, India's Euro I and II performance standards for 
automobiles are designed to help reduce emissions of key vehicle-
related ozone precursors.

Studies of the Effect of Economic Growth on the Environment 
Are Inconclusive:

Both empirical and theoretical studies on the possible connection 
between economic development and environmental quality are inconclusive 
overall. Empirical studies, which analyze historical data for possible 
connections between economic growth and environmental quality, have 
found that emissions for some substances initially increase as national 
income rises and then decrease as a certain level of income is reached. 
However, these results are not consistent across all studies and for 
all substances. [Footnote 31] Similarly, theoretical studies, which seek 
to understand the relationship between economic growth and 
environmental quality, do not agree on the major factors underlying 
this relationship. While acknowledging a probable relationship between 
economic growth and environmental quality, the authors of these studies 
caution that economic growth does not automatically result in 
environmental improvement. They explain that, while economic growth may 
enable countries to pay for environmental protection, growth is not by 
itself sufficient to reverse environmental degradation. See appendix V 
for more information on the studies we reviewed.

Empirical Studies of the Relationship between Economic Growth and 
Environmental Quality Yield Mixed Results:

The empirical studies we reviewed did not consistently find a 
relationship that showed pollution initially increasing as per capita 
income increases and then starting to decrease when income rises beyond 
a certain level. However, such a relationship was found more often for 
some types of pollutants than others.

If such a relationship between pollutants and economic growth is 
presented graphically, it would form an "inverted U curve," as shown in 
figure 11. The point where the curve changes from an upward slope--
pollution increasing with income--to a downward slope is called the 
"turning point.":

Figure 11: Hypothetical Inverted U-Shaped Curve, Showing Relationship 
Between Per Capita Income and Environmental Pollution:

[See PDF for image]

[End of figure]

In conducting these studies, researchers typically used various 
measures of environmental quality, such as a specific pollutant or a 
composite measure of environmental quality. [Footnote 32] In addition, 
to measure economic growth, the studies commonly used per capita 
income, and in most cases, the income levels were converted to 1985 
U.S. dollars either by exchange rates or purchasing power parity 
rates. [Footnote 33] The per capita income level for the United States 
for 1985 was $16,410 under both the exchange rate and purchasing power 
parity methods; for Japan, it was $10,900 for the former and $12,340 
for the latter; for Mexico, $2,180 and $4,745; and for China, $280 and 
$785.

While overall the results of the studies are not consistent regarding 
an "inverted U curve" relationship between pollution and economic 
growth, they are more consistent in showing this relationship between 
pollutants with localized and near-term effects, such as sulfur dioxide 
and particulate matter. On the other hand, studies of substances with 
global and long-term effects, such as carbon dioxide, sometimes did not 
find a turning point or found a turning point beyond the income levels 
of the countries in the study.

For example, as shown in figure 12, the estimated turning point for 
sulfur dioxide in the studies we reviewed using the purchasing power 
parity method was typically in the range of $4,000 to $11,000.[Footnote 
34] While these estimated turning points were higher than per capita 
incomes in China and Mexico, they were generally below the per capita 
incomes in Japan and the United States in 1985. In addition, some 
estimated turning points for particulate matter were in the range of 
$3,000 to $10,000, which is less than per capita incomes in Japan, 
Mexico, and the United States. However, not all the studies we reviewed 
found a turning point for pollutants with localized effects. 
Specifically, one study found a turning point for sulfur dioxide at a 
per capita income level far higher than any country's level in 1985, 
and another study did not find a turning point for particulate matter. 
The studies of carbon dioxide we reviewed either estimated a turning 
point in the range of $10,000 to $63,000, which is above the per capita 
income level of most countries, except for a few developed countries, 
or found that there was no turning point (for example, because 
emissions and per capita incomes increased together).

Figure 12: Estimated Turning Points Found in Selected 
Studies of Particulate Matter, Sulfur Dioxide, and Carbon Dioxide:

[See PDF for image]

Note: Cole-1 and Cole-2 from Cole, Rayner, and Bates, "The 
Environmental Kuznets Curve: An Empirical Analysis," Environment and 
Development Economics (1997)--estimates from two models; Panayotou from 
Panayotou, Sachs, and Peterson, "Developing Countries and the Control 
of Climate Change: Empirical Evidence," Discussion Paper #45, Harvard 
Institute for International Development (1999); Schmalensee from 
Schmalensee, Stoker, and Judson, "World Carbon Dioxide Emissions: 1950-
2050, "Review of Economics & Statistics (1998); Selden-1 and Selden-2 
from Selden and Song, "Environmental Quality and Development: Is There 
a Kuznets Curve for Air Pollution Emissions?," Journal of Environmental 
Economics and Management (1994)--two models estimated; Shafik from 
Shafik, "Economic Development and Environmental Quality: An Econometric 
Analysis," Oxford Economic Papers (1994); Stern from Stern and Common, 
"Is There an Environmental Kuznets Curve for Sulfur?," Journal of 
Environmental Economics and Management (2001).

[End of figure]

Researchers suggested reasons an "inverted U" relationship is found 
more often for sulfur dioxide and particulates than for carbon dioxide. 
For example, they noted that the possible costs of climate change due 
to increased carbon dioxide emissions are borne globally and by future 
generations rather than locally and currently. Furthermore, the 
awareness of the problem of climate change is more recent than the 
awareness of the health effects associated with sulfur dioxide and 
particulates; policies to control carbon dioxide emissions were 
generally not in effect during the period of time analyzed by these 
studies.

Various Theoretical Explanations Have Been Suggested for 
the Relationship of Economic Growth and Environmental Quality:

Other studies have sought to understand the factors underlying the 
relationship between economic growth and environmental quality. These 
studies generally agree that income is a proxy for a number of other 
factors that may be influencing environmental quality as countries 
develop economically. These factors include, for example, changes in a 
country's economic structure, international trade, and a country's 
preference for environmental quality. Nevertheless, researchers do not 
agree on the importance and role of any single factor. These three 
factors are discussed below.

* Changes in a country's economic structure. Some studies pointed out 
that the relationship between economic growth and environmental quality 
reflects changes in an economy's structure as economies develop and is 
not directly due to changes in income. Initially, these studies note, 
economies are primarily agrarian and produce little pollution. As these 
economies grow, the share of national output based on agriculture 
decreases, while the share based on more pollution-intensive 
manufacturing increases; hence pollution increases. At the later stages 
of development, the share of national output based on manufacturing 
decreases, while the share based on less pollution-intensive services 
increases; hence, pollution decreases.

* The role of trade. Other studies noted that international trade can 
affect patterns of production and environmental quality. That is, trade 
allows economically developed countries to emphasize cleaner types 
of industries and to rely on imports from less-developed countries 
for goods produced by more polluting industries. As a result, the 
improvement in some developed countries' environmental indicators is 
partly due to the contraction of their more polluting industries and 
the transfer of these industries to the less developed countries. 
However, researchers also observed that this process--and consequent 
improvement in environmental quality--cannot continue indefinitely 
because the relocation of polluting industries to other countries 
cannot continue indefinitely. [Footnote 35]

* Preference for environmental improvement. According to still other 
studies, the relationship between economic growth and environmental 
quality reflects a country's preference for environmental improvement. 
That is, environmental improvement could be described as a "luxury 
good," that is, a good that people will seek more of as their incomes 
grow beyond subsistence level. Thus, in countries living at subsistence 
levels, pollution is accepted as a side effect of economic development, 
and people are not willing to reduce their consumption of basic 
necessities in order to set aside resources for environmental 
protection. However, as a country's economy grows and incomes increase, 
people become more willing to divert a portion of their resources from 
current consumption to improve the environment. This economic growth, 
in turn, leads to stronger support for environmental legislation and 
new regulations to protect the environment.

Studies have also discussed other factors---such as technology, 
population density, political environment, and environmental 
regulations--that may play key roles in shaping environmental quality 
as economies grow. Regardless of their views, researchers generally 
agree that better data and more detailed research are needed to 
conclusively identify the factors that either directly, or indirectly 
through per capita income, influence environmental quality.

Conclusions:

Of the three substances we reviewed, sulfur dioxide emissions have 
received the most attention in the countries we examined. All of these 
countries have undertaken at least some measures to reduce sulfur 
dioxide emissions. Past trends and projections in all countries seem to 
be affected by economic growth and health concerns. The economically 
developed countries began this process much earlier--as far back as the 
1970s or 1980s--and they have been more successful thus far in 
realizing reductions than the three developing countries. In the 
developing countries, sulfur dioxide emissions declined (though in 
China and Mexico they have started to increase again), but they may 
decrease in the future if new policies are implemented and well 
enforced. While data on sulfur dioxide are far from complete, they are 
more readily available from country sources than data on the other two 
substances, particularly in developing countries. Since sulfate aerosol 
is a climate cooling agent, it is likely that reductions in sulfur 
dioxide emissions will result in some warming, at least at a 
regional level.

Black carbon is being addressed indirectly through measures designed 
to reduce particulate matter in all of the developed countries and to a 
lesser extent in the developing countries. Emissions have begun to 
decline in developed countries, with the exception of Japan, according 
to the database we used, largely as a result of regulations limiting 
diesel fuel emissions, the major source of developed countries' black 
carbon. Developing countries have not seen comparable declines in black 
carbon emissions, because home heating and cooking largely rely on 
burning coal and wood. Because small coal-or wood-burning stoves are 
widely used in these countries, black carbon emissions are more widely 
dispersed than, for example, sulfur dioxide emissions, which are 
usually associated with large power plants. Consequently, developing 
countries may find it challenging to control emissions of black carbon, 
at least for the foreseeable future. In addition, forest burning and 
land-clearing, major sources of black carbon emissions, are more 
prevalent in developing countries. Reliable measurements of black 
carbon from all seven countries are sparse.

Tropospheric ozone levels are difficult to reduce because they result 
from emissions of precursor substances produced by a very diverse range 
of sources. Nevertheless, developed countries have had some success 
over the past decade in reducing high ozone levels, particularly in 
major urban and suburban areas. This trend is likely to continue over 
the next two decades, but ozone concentrations in developing countries 
may continue to rise along with industrialization for the foreseeable 
future. The developing countries we analyzed are only starting to take 
measures to reduce ozone and its precursor substances. Consequently, 
ozone levels in the free troposphere are likely to increase globally as 
a result of a net increase in emissions of its precursors at the 
surface. Methane is expected to play a particularly important role in 
the formation of ozone in the future.

The results of economic research do not convincingly establish whether 
a country's environmental pollution initially increases and then, with 
economic growth, decreases. This type of relationship seems to apply to 
some types of pollutants but not to others. Researchers generally 
agree, however, that unless the incentives facing producers and 
consumers change with higher incomes, pollution will continue to 
increase as economies grow. In other words, income growth, while a 
necessary condition, is not sufficient to reverse environmental 
degradation. Environmental policies must follow to induce appropriate 
responses and turn the pollution path around.

Agency Comments:

We provided a draft of this report to the Secretary of Energy and the 
Administrator of EPA for review and comment. The agencies provided 
written clarifying comments, which we incorporated where appropriate.

As arranged with your offices, we plan no further distribution of this 
report for 30 days after the date of this letter, unless you publicly 
announce its contents earlier. At that time, we will send copies of 
this report to the Ranking Minority Members of the Committee on Energy 
and Commerce, House of Representatives, and its Subcommittees on Energy 
and Air Quality and Oversight and Investigations; the Secretary of 
Energy; the Administrators of the Environmental Protection Agency, 
National Aeronautics and Space Administration, and National Oceanic and 
Atmospheric Administration; the Director, National Science Foundation; 
the Director, Climate Change Science Program Office; and other 
interested parties. We will make copies available to others upon 
request. In addition, copies of this report are available at no cost at 
our Web site, www.gao.gov.

If you have any questions about this report, please contact me at 
(202) 512-3841. Key contributors to this report are listed in 
appendix VI.

John B. Stephenson 

Director, Natural Resources  and Environment:

Signed by John B. Stephenson: 

[End of section]

Appendixes:

Appendix I: Scope and Methodology:

To obtain information on recent research relating to the climate 
change characteristics of the three substances, we contacted scientists 
in four federal agencies: the Department of Commerce's National Oceanic 
and Atmospheric Administration; the Department of Energy; the 
National Aeronautics and Space Administration; and the National 
Science Foundation. These scientists were recommended by staff at 
the U.S. Climate Change Science Program, an interagency research 
coordinating body.

In analyzing trends for the three pollutants, we found that the 
availability and quality of data varied considerably, especially in 
developing countries. Except for countries that are members of the EU 
or participate in the CLRTAP, governments are not required to report 
their emissions of these substances internationally. [Footnote 36] We 
found no standardized system for calculating and reporting emissions. 
Moreover, some of the data reported here are based on direct 
measurements, while others are estimated using proxy data (such as fuel 
use information), which may be less exact than measured data. Most of 
the data used in this study, except where noted, are taken from 
government sources. Dr. Tami Bond of the National Center for 
Atmospheric Research; Dr. Loretta Mickley of Harvard University; 
Dr. Michael Prather of the University of California, Irvine; and Dr. 
David Streets of Argonne National Laboratory provided comments and 
insights on certain sections of the report. The information on foreign 
countries' emissions levels and legislation does not reflect our 
independent analysis.

To obtain information on policies and measures, we first sought a 
comprehensive source of information for each country. Because we 
found no such source, we contacted government, academic, and other 
researchers and analysts in the United States and the other countries, 
and the countries' embassies in the United States. We also gathered 
information from government publications, web sites, e-mail 
correspondence with U.S. and foreign government officials, and 
discussions with embassy personnel. While we tried to make this report 
as complete as possible, there may be additional policies and programs 
underway that are not addressed here.

To assess the literature on the relationship between economic growth 
and environmental pollution, we conducted computerized literature 
searches to identify relevant articles. To help us determine which 
articles to focus on, we sought guidance from recognized experts who 
specialize in this field. The extent of governmental action to control 
a specific pollutant is believed to be one important factor--but not 
the only factor--in explaining the relationship between economic growth 
and emissions of that pollutant. Therefore, even though few countries 
have acted to control carbon dioxide emissions and have done so 
recently, we included studies that examined the relationship between 
economic growth and such emissions.

We conducted our review between October 2001 and April 2003 in 
accordance with generally accepted government auditing standards.

[End of section]

Appendix II: Programs and Measures to Reduce Emissions of 
Sulfur Dioxide:

Country: United States: 

Measures: Section 109 of the Clean Air Act requires EPA to 
establish National Ambient Air Quality Standards (NAAQS) for air 
pollutants that may endanger public health and welfare. EPA established 
such NAAQS for sulfur dioxide. Under the 1990 amendments, areas not in 
attainment with the NAAQS must meet special compliance schedules.

Measures: Section 110 of the Clean Air Act requires states to 
adopt plans, known as State Implementation Plans (SIP), which detail 
the regulations a state will use to implement, maintain, and enforce 
the NAAQS. EPA must approve each SIP, and if a SIP is not acceptable, 
EPA may take over enforcement of the Clean Air Act in that state.

Measures: Section 111 of the Clean Air Act requires EPA to 
establish nationally uniform, technology-based standards called New 
Source Performance Standards for categories of new industrial 
facilities, such as power plants, steel mills, and smelters. These 
standards limit the amount of certain pollutants, including sulfur 
dioxide, that may be emitted.

Measures: Sections 160-169 of the Clean Air Act establish 
requirements for the prevention of significant deterioration (PSD) of 
air quality in areas that have attained the NAAQS. The act divides 
clean air areas into three classes and specifies the increments of 
sulfur dioxide and particulate matter pollution allowed in each. In 
order to receive a PSD permit, a new or modified major source of 
pollution must show that it will not contribute to a violation of the 
increments or of the national ambient air quality standards and that it 
will use best available control technology (BACT). This provision is 
referred to as PSD New Source Review.

Measures: Sections 171-173 of the Clean Air Act establish pre-
construction permitting requirements for major new and modified sources 
in non-attainment areas (areas that have not attained the NAAQS). To 
receive a permit, such sources must, among other things, (1) obtain 
emissions offsets, thereby assuring that reasonable progress toward 
attainment of the NAAQS will occur, and (2) comply with the "lowest 
achievable emissions rate."

Measures: Title IV of the Clean Air Act created 
EPA's Acid Rain Program, which caps sulfur dioxide emissions from 
virtually all U.S. electric power plants at 8.95 million tons. Plant 
operators were required to reduce their emissions through any 
combination of strategies, including installing scrubbers, switching to 
natural gas or low-sulfur coal, or trading emissions allowances. The 
first phase of the program ran from 1995 to 1999, and the second phase, 
with more stringent caps, began in 2000 and will run indefinitely. The 
program features a provision that allows power plants that exceed their 
emissions targets to "bank" extra allowances during the first phase of 
the program and then use these banked allowances during the more 
stringent second phase.

Country: United Kingdom: 

Measures: The United Kingdom's 1956 and 1968 Clean Air Acts, 
among other things: * authorized local councils to set up smokeless 
zones and make grants to householders to convert their homes from 
traditional coal fires to heaters fueled by gas, oil, smokeless coal, 
or electricity; * set limits on sulfur dioxide emissions from small 
power plants; * The United Kingdom's Environment Act of 1995 requires 
the government to produce a national air quality strategy that 
identifies clear, measurable targets for improved air quality in the 
United Kingdom. This strategy is to be developed based on understanding 
of the health effects of the pollutants concerned and costs of emission 
reduction methods and aims to improve air quality by 2005. The strategy 
sets standards and objectives for sulfur dioxide and seven other air 
pollutants. The 1995 act also established a system of local air quality 
management, under which authorities are required to assess the current 
and future quality of air in their areas against the national air 
quality strategy objectives.

Measures: The Convention on Long-Range Transboundary Air 
Pollution (CLRTAP) binds the United Kingdom to reduce sulfur, as do 
certain CLRTAP protocols: * The 1994 Oslo Protocol on Further 
Reduction of Sulfur Emissions, which aims at gradually achieving 
critical loads of sulfur; * The 1999 Gothenburg Protocol, signed but 
not ratified by the United Kingdom, which set emissions ceilings for 
2010 for sulfur dioxide and three other pollutants, is expected to 
enter into force as early as 2003. (CLRTAP covers more European 
countries than the EU, but the EU directives generally require more 
ambitious emissions reductions than the CLRTAP protocol.).

Measures: EU directives which require the United 
Kingdom to reduce sulfur dioxide emissions include: * The First 
Daughter Directive (1999/30/EC), under which EU members must establish, 
and achieve by 2005, a legally binding limit on concentrations of 
sulfur dioxide and three other substances; * The Directive on the 
Incineration of Wastes (2000/76/EC), which sets limits on emissions of 
sulfur dioxide and other substances from waste incineration plants; * 
The Large Combustion Plant Directive (2001/80/EC), which sets limits on 
sulfur dioxide and nitrogen oxides from combustion plants with a 
thermal input of 50 megawatts or greater.

Country: Germany: 

Measures: * The Large Combustion Ordinance contains 
emissions ceilings for new power plants in Germany; * The CLRTAP 
requirements and EU directives also apply to Germany.

Country: China: 

Measures: The Air Pollution Control Law, enacted in 1987 and 
amended in 2000, aims to improve air quality in key urban areas. 
Specifically, it; * broadens the scope of affected industries beyond 
industrial sources and power plants, to include automobiles, ships, 
domestic heating, and cooking stoves;; * provides an incentive for 
using high-quality, low-sulfur coal and renewable energy;; * allows so-
called "priority cities" to designate zones within which all burning of 
high-polluting fuel (i.e., coal) can be prohibited and calls for the 
phase-out of a form of dirty coal in large-and medium-sized cities;; * 
requires new or expanded sulfur dioxide-emitting power plants or large-
and medium-sized industrial enterprises to install desulfurization 
equipment; and; * encourages cities to replace individual household 
coal heating stoves with centralized district heat.

Measures: The Energy Conservation Law, which entered into 
force in January 1998, promotes energy conservation and efficiency. 
Other energy conservation laws also exist.

Measures: A fuel tax has been imposed on high-sulfur coals, 
and between January and September 2000, 4,732 mines producing high-
sulfur coal were closed.

Measures: Subsidies for coal have been greatly reduced since 1984.

Source: GAO.

[End of table]

[End of section]

Appendix III: Programs and Measures to Reduce Emissions of Black Carbon 
or Particulate Matter:

Country: United States: 

Measures: The Heavy Duty Diesel Rule, 
promulgated in 2001, will require significant future reductions in 
highway diesel engine particulate matter emissions. It will also 
require diesel oil refiners to reduce most sulfur from diesel fuel by 
2006 in preparation for new engines in 2007. In 2030, when the rule is 
fully implemented, it is expected that particulate matter from diesel 
vehicles will be reduced by 130,000-140,000 tons per year relative to 
1996.

Country: United States: 

Measures: The Smoke Control Act of 1993 empowers local 
authorities to declare a smoke control area if it appears that air 
quality standards will not be met. Under the law, the local government 
can require that only certain fuels be used for domestic heating.

Measures: EU directives aimed at reducing particulate 
matter include: * Directive 1998/70/EC, which sets the maximum 
allowable sulfur content of gasoline and diesel fuel; * The First 
Daughter Directive (1999/30/EC), which contains a particulate matter 
standard for the EU countries; * The Directive on the Sulfur Content 
of Certain Liquid Fuels (1999/32/EC), which mandates reductions in 
sulfur content of diesel fuel to enhance performance of emissions-
reduction devices; * Directive 1999/96/EC, which sets the emission 
limit values and implementation dates in two stages for heavy duty 
vehicles (Euro III and IV). The standards cover emissions of 
particulate matter and ozone precursors.

Country: Germany: 

Measures: The EU directives described above also apply to Germany.

Country: China: 

Measures: Euro I and II standards for the control of emissions from 
diesel vehicles.

Country: India: 

Measures: Euro I and II standards for the control of emissions from 
diesel vehicles.

Source: GAO.

[End of table]

[End of section]

Appendix IV: Programs and Measures to Reduce Ground-Level Ozone:

Country: The United States: 

Measures: The Clean Air Act has resulted in the creation of 
several trading programs for reducing nitrogen oxide emissions in the 
electric utility sector: * EPA's Acid Rain Program sets emissions 
rates for all affected utilities. Unlike sulfur dioxide, there is no 
cap on total nitrogen oxide emissions, but utilities may choose to 
over-control at units where it is easier to do so and average these 
emissions with those at their other units, thereby achieving overall 
emissions reductions at lower costs; * The EPA Nitrogen Oxides SIP 
Call[A] requires 19 states and the District of Columbia to reduce total 
nitrogen oxide emissions from utilities by a certain number of tons 
each year; compliance for Phase I must be achieved no later than May 
31, 2004. Power producers subject to these regulations are allowed to 
trade emissions allowances to meet the required limits; * The Nitrogen 
Oxides Budget Trading Program, begun in 1999 in nine Northeastern 
states, aims to reduce nitrogen oxide emissions during the summer 
months to enable states to attain the standard for ground-level ozone. 
Like the programs above, it is a cap and trade program, under which 
total emissions are capped, and affected parties may trade emissions 
allowances.

Measures: The Clean Air Act has also provided the framework 
for ozone-reducing reductions in the transportation sector. The most 
recent regulation with significant impact on transportation sector 
ozone precursors is the Tier 2 program, which was promulgated in 2000 
and will be phased in starting in 2004, when refiners must produce low-
sulfur fuel for passenger vehicle gasoline. Tier 2 also sets tailpipe 
emission standards for all classes of passenger vehicles, including 
sport utility vehicles and light-duty trucks.

Measures: A Clean Air Act regulation requires the combustion 
of methane and other non-methane organic compounds from large 
landfills. The regulation also contains a performance standard based on 
the allowable concentration of methane measured at the landfill; In 
addition to programs regulating emissions from cars and trucks, EPA 
regulates emissions of nitrogen oxides and hydrocarbons from aircraft, 
ships, locomotives, recreational vehicles, off-road diesel equipment 
(e.g., farm and construction equipment), and spark-ignition engines, 
such as chain saws, lawn mowers, and forklifts.

Measures: The U.S. Department of Transportation administers a 
program called "Congestion Mitigation and Air Quality Improvement" 
aimed at reducing ozone and its precursors (as well as particulate 
matter) by funding new transit services, bicycle, and pedestrian 
improvement, alternative fuel projects, traffic-flow improvements, and 
other emissions-reducing projects.

Measures: In the industrial sector, the Clean 
Air Act specifies performance standards for new industrial sources. 
The standards, called New Source Performance Standards, establish 
maximum emission levels for new or modified major stationary sources, 
such as steel mills and smelters. These standards also apply to 
power plants.

Country: United Kingdom: 

Measures: CLRTAP Protocols that bind the United Kingdom and 
other European countries include: * The 1988 Sofia Protocol, which set 
a target for emissions of nitrogen oxides; * The 1991 Geneva Protocol, 
which requires a reduction in emissions of volatile organic compounds; 
* The 1999 Gothenburg Protocol, signed but not ratified by the United 
Kingdom, which sets emissions ceilings for nitrogen oxides, volatile 
organic compounds, and two other substances.

Measures: The EU directives aimed at reducing ozone and/or its 
precursors include: * Directives on Air Pollution by Ozone (92/72/EC 
and 2002/3/EC), which establish thresholds for ozone and require that 
threshold exceedances must be reported to the EU Commission and to the 
public; * The Directive on VOC Emissions from the Storage of Petrol 
(94/63/EC), which sets guidelines for reducing volatile organic 
compound emissions from the storage and distribution of petrol 
(gasoline) from terminals to service stations; * The Framework 
Directive (96/62/EC), which established the framework under which the 
EU countries would agree on emissions limits for certain pollutants. 
The Directive requires that, if limits are exceeded, member states 
devise abatement programs to reach the limits within a set deadline; * 
The Directive 98/69/EC, which establishes emission limit values and 
implementation dates in two stages for light-duty vehicles (Euro III 
and IV). The standards cover ozone precursors and particulate matter; 
* The First Daughter Directive (99/30/EC), which sets limit values for 
nitrogen oxides (and other substances.); * The VOC Solvents Directive 
(99/13/EC), which limits emissions of volatile organic compounds; * 
The Directive on Landfills (99/31/EC), which aims to harmonize controls 
on the landfill of waste throughout the EU. Its main focus is on common 
standards for the design, operation and aftercare of landfill sites. It 
also aims to reduce the amount of methane emitted from landfill sites; 
* The Large Combustion Plant Directive (2001/80/EC), which sets limits 
on sulfur dioxide and nitrogen oxides from combustion plants with a 
thermal input of 50 megawatts or greater.

Measures: The National Emission Ceiling Directive 
(2001/81/EC), which sets ceilings for emissions of nitrogen oxides, 
sulfur dioxide, ammonia, and volatile organic compounds to be attained 
by 2010. (As of early 2003, this protocol was not yet in force.).

Country: Germany: 

Measures: The CLRTAP requirements and EU directives cited 
above apply to Germany.

Country: Japan: 

Measures: The Air Pollution Control Law requires stations in 
several parts of the country to monitor for nitrogen dioxide, suspended 
particulate matter, sulfur dioxide, carbon monoxide, and photochemical 
oxidants. It also establishes maximum permissible limits on exhaust 
gases from motor vehicles.

Measures: The Automobile Nitrogen Oxides Law sets the 
fundamental policies and plans for reducing the total volume of 
nitrogen oxides for specific automobiles.

Country: China: 

Measures: Although the government does not require the 
reporting of data on ozone concentrations, the city of Beijing does so 
when ozone levels become particularly high.

Measures: Euro I and II standards for the control of 
motor vehicle emissions, including carbon monoxide, hydrocarbons, and 
nitrogen oxides.

Country: Mexico: 

Measures: Mexico's Tag Zero Program offers a 2-year 
exemption from Mexico City's "car-free" policy for drivers of clean 
cars. Under the program, drivers of new cars or cars that have been 
upgraded with catalytic converters may drive in the city any day of the 
week, while owners of cars without such certification may drive on only 
a certain number of days per week. (An exempted, or clean, car is 
denoted by a zero on a sticker placed on the back window of the car. 
The car's license plate indicates the days a car may not be driven if 
it does not have a sticker.) The Tag Zero program thus rewards the 
purchase of clean vehicles.

Country: India: 

Measures: Euro I and II standards for the control of 
motor vehicle emissions, including carbon monoxide, hydrocarbons, and 
nitrogen oxides.

Source: GAO.

[A] The Nitrogen Oxides SIP Call is authorized under section 110 of the 
Clean Air Act. A SIP is a State Implementation Plan, which is a 
proposal submitted by each state to EPA containing emission limitations 
and other control measures to attain, maintain, and enforce the NAAQS. 
EPA may issue a SIP Call under the act when it finds that the 
applicable SIP fails to comply with a requirement of the act. The SIP 
Call requires the state to revise its SIP.

[End of table]

[End of section]

Appendix V: Summary of Results of Selected Studies on Economic Growth 
and Environmental Pollution:

The following table presents information on the studies of economic 
growth and environmental quality that we reviewed.

Table 2: Results of Selected Studies of Economic Growth and 
Environmental Quality:

Based on exchange rates: 

Study's author(s) and year: Grossman and 
Krueger, "Economic Growth and Environment," Quarterly Journal of 
Economics (1995); Estimated per capita income for turning points, 
by type of emission[A]: Particulate matter: None found[B]; Estimated 
per capita income for turning points, by type of emission[A]: Sulfur 
dioxide: $4,100; Estimated per capita income for turning points, 
by type of emission[A]: Carbon dioxide: Not studied.

Study's author(s) and year: Holtz-Eakin and 
Selden, "Stoking the Fires? CO2 Emissions and Economic Growth," Journal 
of Public Economics (1995); Estimated per capita income for turning 
points, by type of emission[A]: Particulate matter: Not studied; 
Estimated per capita income for turning points, by type of emission[A]: 
Sulfur dioxide: Not studied; Estimated per capita income for turning 
points, by type of emission[A]: Carbon dioxide: $35,400[C].

Study's author(s) and year: Panayotou, 
"Demystifying the Environmental Kuznets Curve: Turning a Black Box into 
a Policy Tool," Environment and Development Economics (1997); Estimated 
per capita income for turning points, by type of emission[A]: 
Particulate matter: Not studied; Estimated per capita income for 
turning points, by type of emission[A]: Sulfur dioxide: 5,000; 
Estimated per capita income for turning points, by type of emission[A]: 
Carbon dioxide: Not studied.

Study's author(s) and year: Roberts and 
Grimes, "Carbon Intensity and Economic Development 1962-91: A Brief 
Exploration of the Environmental Kuznets Curve," World Development 
(1997); Estimated per capita income for turning points, by type of 
emission[A]: Particulate matter: Not studied; Estimated per capita 
income for turning points, by type of emission[A]: Sulfur dioxide: Not 
studied; Estimated per capita income for turning points, by type of 
emission[A]: Carbon dioxide: None found.

Based on purchasing power parity: 

Estimated per capita income for turning points, by type of emission[A]: 
Particulate matter: Shafik, "Economic Development and Environmental 
Quality: An Econometric Analysis," Oxford Economic Papers (1994): 
[Empty]; Estimated per capita income for turning points, by type of 
emission[A]: Sulfur dioxide: Shafik, "Economic Development and 
Environmental Quality: An Econometric Analysis," Oxford Economic 
Papers (1994): [Empty]; Estimated per capita income for turning points, 
by type of emission[A]: Carbon dioxide: Shafik, "Economic Development 
and Environmental Quality: An Econometric Analysis," Oxford Economic 
Papers (1994): [Empty].

Study's author(s) and year: Shafik, "Economic 
Development and Environmental Quality: An Econometric Analysis," 
Oxford Economic Papers (1994); Estimated per capita income for turning 
points, by type of emission[A]: Particulate matter: $3,300; Estimated 
per capita income for turning points, by type of emission[A]: Sulfur 
dioxide: 3,700; Estimated per capita income for turning points, by type 
of emission[A]: Carbon dioxide: Not studied.

Study's author(s) and year: Selden and Song, 
"Environmental Quality and Development: Is There a Kuznets Curve for 
Air Pollution Emissions?," Journal of Environmental Economics and 
Management (1994)--two models estimated; Estimated per capita income 
for turning points, by type of emission[A]: Particulate matter: 9,600; 
9,800; Estimated per capita income for turning points, by type of 
emission[A]: Sulfur dioxide: 10,700; 8,900; Estimated per capita income 
for turning points, by type of emission[A]: Carbon dioxide: Not 
studied.

Study's author(s) and year: Cole, Rayner, and 
Bates, "The Environmental Kuznets Curve: An Empirical Analysis," 
Environment and Development Economics (1997)--two models estimated; 
Estimated per capita income for turning points, by type of emission[A]: 
Particulate matter: 7,300; 8,100; Estimated per capita income for 
turning points, by type of emission[A]: Sulfur dioxide: 5,700; 6,900; 
Estimated per capita income for turning points, by type of emission[A]: 
Carbon dioxide: 25,100; 62,700.

Study's author(s) and year: Schmalensee, 
Stoker, and Judson, "World Carbon Dioxide Emissions: 1950-2050," Review 
of Economics & Statistics (1998); Estimated per capita income for 
turning points, by type of emission[A]: Particulate matter: Not 
studied; Estimated per capita income for turning points, by type of 
emission[A]: Sulfur dioxide: Not studied; Estimated per capita income 
for turning points, by type of emission[A]: Carbon dioxide: 10,000.

Study's author(s) and year: Unruh and Moomaw, 
"An Alternative Analysis of Apparent EKC-type Transitions," Ecological 
Economics (1998); Estimated per capita income for turning points, 
by type of emission[A]: Particulate matter: Not studied; Estimated per 
capita income for turning points, by type of emission[A]: Sulfur 
dioxide: Not studied; Estimated per capita income for turning points, 
by type of emission[A]: Carbon dioxide: None found.

Study's author(s) and year: Panayotou, Sachs, 
and Peterson, "Developing Countries and the Control of Climate Change: 
Empirical Evidence," Discussion Papers #45, Harvard Institute for 
International Development (1999); Estimated per capita income for 
turning points, by type of emission[A]: Particulate matter: Not 
studied; Estimated per capita income for turning points, by type of 
emission[A]: Sulfur dioxide: Not studied; Estimated per capita income 
for turning points, by type of emission[A]: Carbon dioxide: 12,000.

Study's author(s) and year: Stern and Common, 
"Is There an Environmental Kuznets Curve for Sulfur?" Journal of 
Environmental Economics and Management (2001); Estimated per capita 
income for turning points, by type of emission[A]: Particulate matter: 
Not studied; Estimated per capita income for turning points, by type of 
emission[A]: Sulfur dioxide: 101,200[D]; Estimated per capita income 
for turning points, by type of emission[A]: Carbon dioxide: Not 
studied.

Source: GAO.

[A] All numbers are in 1985 dollars unless otherwise noted.

[B] Grossman and Krueger estimated a turning point separately for heavy 
particulate and smoke. While no turning point for heavy particulate was 
found, the turning point for smoke was $6,200.

[C] In 1986 dollars.

[D] In 1990 dollars.

[End of table]

[End of section]

Appendix VI: GAO Contact and Staff Acknowledgments:

GAO Contact:

David Marwick, (202) 512-6775:

Acknowledgments:

In addition to the individual named above, Bernice H. Dawson, Richard 
A. Frankel, Anne K. Johnson, Mehrzad Nadji, and Carol Herrnstadt 
Shulman made key contributions to the report. Important contributions 
were also made by Laura Yannayon and Katherine M. Raheb.

(360150):

FOOTNOTES

[1] Intergovernmental Panel on Climate Change (IPCC), 2001. Climate 
Change 2001: The Scientific Basis. Contribution of Working Group I to 
the Third Assessment Report of the Intergovernmental Panel on Climate 
Change. Cambridge University Press, Cambridge, United Kingdom and New 
York, New York.

[2] Oxidation is a type of chemical reaction involving oxygen.

[3] Wherever it is found, ozone is chemically the same, a molecule 
comprised of three oxygen atoms. Its effects depend on its location. In 
the earth's upper atmosphere (called the stratosphere), ozone is 
beneficial because it prevents ultraviolet radiation--which is 
dangerous to human health--from reaching the earth's surface. However, 
at lower levels (called the troposphere), it is harmful to human 
health. Ozone in the stratosphere also has impacts on climate. It is 
formed by different means than ozone in the troposphere. We do not 
discuss stratospheric ozone at length in this report because it is 
produced mainly through natural (non-human-induced) processes. Unless 
otherwise stated, when we refer to ozone, we are referring to 
tropospheric ozone.

[4] The Montreal Protocol, ratified by the United States in 1988, aims 
to reduce the use of substances that deplete stratospheric ozone. Among 
these substances are chlorofluorocarbons, which are also potent 
greenhouse gases.

[5] Sulfur hexafluoride and perfluorocarbons, which are man-made 
greenhouse gases, have atmospheric lifetimes of several thousand years. 
They are not depicted in figure 1.

[6] Isoprene and monoterpenes are examples of volatile organic 
compounds produced by vegetation.

[7] IPCC's Third Assessment Report, 2001.

[8] The United Kingdom includes Great Britain (England, Scotland, and 
Wales) and Northern Ireland.

[9] The United States is party to some, but not all, of the CLRTAP 
protocols. Certain of the protocols extending the convention are not 
yet in force.

[10] V. Ramanathan et al. "Aerosols, Climate, and the Hydrological 
Cycle." Science, 294, Dec. 7, 2001.

[11] Ozone in the stratosphere also has impacts on climate. It is 
formed by different means than ozone in the troposphere. We do not 
discuss stratospheric ozone at length in this report because it is 
produced mainly through natural (non-human-induced) processes. Ozone in 
the troposphere exists in two zones, the boundary layer and the free 
troposphere. The significance of these zones is explained in the next 
section.

[12] Arlene Fiore et al. "Linking Air Pollution and Climate Change: The 
Case for Controlling Methane." Geophysical Research Letters, 29(19), 
1919, 2002.

[13] Michael Prather et al. "Fresh Air in the 21st Century?" 
Geophysical Research Letters, 30(2), 1100, 2003.

[14] In this report, we use sulfur dioxide emissions as a proxy for 
sulfate aerosols. This is because sulfate aerosols are the result of 
the chemical transformation in the atmosphere of sulfur dioxide 
emissions, such as those from power plants and other sources. It is 
difficult to attribute sulfate aerosols in the atmosphere to individual 
countries, but such attribution is possible with sulfur dioxide because 
many countries keep track of their sulfur dioxide emissions.

[15] Because ozone is not emitted directly, it is measured in terms of 
concentrations.

[16] Flue gas desulfurization equipment removes sulfur oxides from the 
combustion gases of a boiler plant before it discharges them to the 
atmosphere.

[17] Four scenarios with reductions ranging from 7 to 37 percent were 
prepared by Dr. T. Matsui for the United Nations Environment Program. 
The data for Japan in figure 4 show projected emissions reductions in 
2010 from an intermediate scenario.

[18] T.C. Bond and D.G. Streets, "Draft Global Black Carbon Inventory," 
2002. Dr. Tami Bond, Visiting Scientist, National Center for 
Atmospheric Research, and Dr. David Streets, Senior Scientist, Argonne 
National Laboratory, provided both data and commentary on this section.

[19] Particulate matter is the general term used for a mixture of solid 
particles and liquid droplets found in the air. It comes from vehicle 
emissions, dust, fires, sea salt, and black carbon (soot) from wood and 
coal burning. Particulate matter can be either coarse or fine. Coarse 
particulate matter is referred to as PM10 because the particles have a 
diameter of 10 micrometers or less. Fine particles, referred to as 
PM2.5, have a diameter of 2.5 micrometers or less. Black carbon is a 
component of PM2.5, but this fraction may vary across countries, 
depending on fuel sources. Secondary particles can be formed in the 
atmosphere from gaseous emissions. For example, sulfates are a form of 
particulate matter.

[20] The 2002 Heavy-duty Diesel Engine Rule is aimed at reducing 
emissions from heavy-duty trucks.

[21] EPA's estimate of black carbon emissions for 1996 differs from 
that found in the Bond and Streets database. This is because estimates 
from the two studies are based on different assumptions.

[22] The sulfur content of diesel fuel is important because sulfur can 
impair the performance of a vehicle's emissions-reducing device.

[23] Coke is a solid carbonaceous residue derived from low-ash, low-
sulfur bituminous coal. It is used as a fuel (and as a reducing agent) 
for smelting iron ore in blast furnaces.

[24] Levels of emissions from biofuels are particularly uncertain 
because data are so sparse. Estimates in the Bond and Streets database 
are calculated based largely on a limited number of fuel use surveys 
combined with socioeconomic data.

[25] Dr. Loretta J. Mickley, Research Associate, Atmospheric Chemistry, 
Division of Engineering and Applied Sciences, Harvard University, and 
Dr. Michael Prather, Fred Kavli Chair and Professor, Department of 
Earth System Science, University of California Irvine, provided 
insights and comments on this section.

[26] Ozone has a shorter life span in the boundary layer because 
processes in that layer can destroy ozone, but these same processes do 
not occur in the free troposphere. The processes include deposition and 
chemical destruction at night.

[27] There are various definitions of background ozone. As used in this 
report, background ozone refers to ozone that is produced by human 
sources as well as lesser amounts from natural precursor sources--such 
as volatile organic compounds from vegetation or nitrogen oxides from 
lightning--that travels into a given jurisdiction from elsewhere and 
is not associated with local emissions.

[28] We use projections prepared by Dr. L.J. Mickley of Harvard 
University's Atmospheric Chemistry Modeling Group. The Harvard model 
has been cited in the IPCC Third Assessment Report, a peer-reviewed 
document. (The IPCC is the premier scientific organization devoted to 
assessing climate change.) The projections were produced using a 
general circulation (climate) model and depict expected global average 
ozone concentrations in the free troposphere in 2025. For comparison 
purposes, we also include a map showing tropospheric ozone 
concentrations in 1990. The Harvard projections are based on the IPCC 
Special Report on Emissions Scenarios (IPCC/SRES) A2 Marker Scenario. 
The Harvard model is able to capture in great detail the physical and 
chemical processes leading to tropospheric ozone formation and can also 
show the long-range movement of ozone and its precursors.

[29] Ozone levels are particularly low over most humid equatorial 
regions because, over the humid tropics where nitrogen oxide emissions 
are generally low, water vapor is involved in reactions that destroy 
ozone.

[30] Even though global emissions of methane appear to be slowing, it 
is not clear that they will have dropped sufficiently to result in 
reduced concentrations in the atmosphere.

[31] Carbon dioxide is not regulated as a pollutant in the United 
States.

[32] The source for the environmental data most often used in these 
studies was the Global Environmental Monitoring System, compiled by the 
United Nations, except for data on carbon dioxide emissions from the 
U.S. Oak Ridge National Laboratory. Income data from different 
countries were often adjusted to comparable units in terms of exchange 
rates or purchasing power. In general, the data could be from as many 
as 149 economically developing and developed countries for 1960 through 
2000 or any year during that period. Models differ in the exact 
specification of their equations, such as the number and type of other 
factors that are included in the model (e.g., international trade, 
population density) and the mathematical form of the relationship 
tested.

[33] To compare incomes across countries, incomes are converted to U.S. 
dollars in one of two ways: (1) using the official exchange rate 
between the dollar and the other currency or (2) using purchasing power 
parity rates--an international dollar that has the same purchasing 
power in another country as the dollar has in the United States.

[34] All numbers are presented in 1985 dollars converted by purchasing 
power parity.

[35] The empirical studies we reviewed that examined the role of trade 
on environmental quality did not provide support for the suggestion 
that exporting polluting industries (sometimes called "environmental 
dumping") accounts for the observed reduction in some pollutants in 
developed countries.

[36] Under the Framework Convention on Climate Change, developed (Annex 
I) countries generally report their emissions of sulfur dioxide along 
with their emissions of the six conventional greenhouse gases. This is 
the source of our data on Japanese sulfur dioxide emissions.

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