The first time
Stephen Conley flew through the plume of natural gas
hovering above
Aliso
Canyon, California, he knew the situation was bad. He
couldn’t see the methane or ethane pouring out from the old
well, but he could smell the rotten-egg odor of the
mercaptan added to natural gas to warn people of leaks. “It
was nasty,” he recalls.
And then there were the readings from his plane’s scientific
instrumentation. Conley has flown his specialized research
plane over the sites of many oil and gas leaks in the past.
In normal, leak-free air, he usually detects about 2 parts
per million (ppm) of methane. Over a leak, that might go up
to 4 or 5 ppm. But the air over California in November had
levels of 50 ppm a mile from the leak site.
“That’s when I first got this idea that, holy crap, this is
a big leak,” says Conley, an atmospheric scientist at the
University of California, Davis, and Scientific Aviation.
Now, analysis of Conley's data reveals that by the time the
leak had been plugged, just over 107,000 tons of methane and
8,000 tons of ethane had been released from Aliso Canyon.
That's the equivalent of the greenhouse gas emissions from
half a million cars, spewed into the air near Los Angeles
over the span of 16 weeks.
“On the scale of the control efforts that have been
put in place to minimize greenhouse gas emissions, it
rolls that back years,” says study co-author
Thomas Ryerson, a research chemist at the National
Oceanic and Atmospheric Administration.
Though methane is a powerful greenhouse gas and the
Aliso Canyon event was a “monster” emitter, the event
highlights an even bigger problem, Conley says. There
are hundreds of
natural gas storage facilities like this one around
the country, and there’s nothing in place to monitor
these facilities for leaks or respond to them quickly.
“Even if each one is leaking [a little bit], that’s a
big number,” Conley warns.
The Aliso Canyon leak came from a natural gas storage
facility that had started out its life in 1954 as an oil
well. In 1973, that well was converted into natural gas
storage, a
common practice for U.S. energy companies that need
a place to store the fuel near towns and cities.
On October 23, residents of the nearby town of Porter
Ranch reported smelling a gas leak, and Southern
California Gas Company discovered the leak at Aliso
Canyon. Two weeks later, Conley was tasked by the
California Energy Commission, for whom he had been
working under contract, to fly through the plume above
the leak and map out where and how much methane and
ethane were being emitted.
Conley and his team made 13 flights through the plume
between November 7, two weeks after the leak began, and
February 13, two days after the leak was plugged.
Because the natural gas had been stored in an old oil
well, it also contained small amounts of substances,
such as benzene and toluene, that wouldn’t normally be
found in a natural gas pipeline, says Ryerson. Other
scientists led by
Donald Blake of the University of California,
Irvine, collected samples of the gas down on the ground
and analyzed it back in the lab. Combining that data
with Conley's measurements of methane and ethane gave
the researchers “the DNA of the leak,” Ryerson says.
The team confirmed that efforts to stop the leak had
been successful, though 3 percent of the natural gas
stored in the facility had been lost by that time. The
data also showed that the Aliso Canyon event released
enough methane to make this the largest leak in history
in terms of climate impact, Conley and his colleagues
report this week in Science. Only one previous
event, at Moss Bluff, Texas in 2004, released more
natural gas, but most of that burned off in a huge
fireball.
The leak also released some 2.5 tons of benzene, a
carcinogen, into the atmosphere, they found. That sounds
like a lot, but cars and other sources emit about a
thousand times more every year, Ryerson says.
Individuals who were in the way of the plume may have
been exposed to more worrying amounts of the substance,
but for now there’s no way to know.
Southern California Gas Company has stated that it will
mitigate the greenhouse gas emissions caused by the
leak.
Francesca Hopkins, an Earth systems scientist at
NASA’s Jet Propulsion Laboratory, has some ideas about
how they can do that.
While at UC Irvine, she led a study that mapped out
methane emissions across the LA Basin using a white Ford
Transit van equipped with a snorkel and a host of
scientific equipment. As they
report in the Journal of Geophysical Research:
Atmospheres, her team found methane leaking from
compressed natural gas fueling stations, gas-fired power
plants, landfills—even ones that had been closed for 50
years—and, of course, cows.
Plugging up those “fugitive leaks” could be part of the
gas company's mitigation efforts, Hopkins says. And
targeting methane leaks could bring a far bigger bang
for the buck than carbon dioxide emissions, she says.
While methane has a shorter lifespan in the atmosphere,
it is also a far more potent greenhouse gas and one that
has an economic value, since lost methane is essentially
wasted fuel. Luckily, methane is also a lot easier to
get rid of because it can be burned.
Conley notes that this one leak’s overall contribution
to climate change is just a drop in the bucket. That’s
because there’s already so much carbon dioxide, methane
and other greenhouse gases being released around the
globe. For his team, the real issue is how to prevent
such massive leaks from happening more often and
becoming a bigger climate threat.
“Nobody really knows yet what caused Aliso to happen,”
Ryerson says. If it had happened in a spot more distant
from where people live, it might not have been noticed
for a lot longer. Even then, the team was only able to
measure the magnitude of the event because Conley was
already under contract to the state.
Scientists were also available to map the plumes from
two previous oil and gas disasters—the
Deepwater Horizon oil spill in the Gulf of Mexico in
2010 and a
natural gas leak in the North Sea in 2013—and
provide key information for stopping the events. But
Ryerson and Conley both note that the three situations
were largely due to luck.
“There is no standing capability for a quick-response
airborne chemical measurement” of a disaster, Ryerson
says. They argue that some sort of “grab-and-go package”
should be developed to get scientists to a site within
hours rather than weeks or months.
“We’ve been lucky three times in a row,” Ryerson says.
“We should do something to be ready for the fourth.”
Read more:
http://www.smithsonianmag.com/science-nature/size-california-methane-leak-isnt-scariest-part-story-180958234/#bWGCXriceKYIk7wS.99
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