https://phys.org/news/2019-08-natural-gas-leaks-important-source-greenhouse.html
August 12, 2019
Natural-gas leaks are important source of greenhouse gas emissions in
Los Angeles
by Emily Velasco, California Institute of Technology
In discussions of anthropogenic climate change, carbon dioxide generally
gets the spotlight, but it is not the only greenhouse gas spewed into
the atmosphere by human activity, nor is it the most potent.
Methane is another greenhouse gas that is increasing in Earth's
atmosphere because of humans. Methane is produced by human activity in
much smaller amounts than carbon dioxide, but it is roughly 25 times
more powerful as a greenhouse gas. Though it is often associated with
cow flatulence, bovines are not the only human-associated source of methane.
New research by Caltech scientists shows that, at least in the Los
Angeles Basin, leaks of natural gas used for heating homes and
businesses are major contributors to methane in the atmosphere.
The research was conducted by Liyin He (MS '18), a graduate student in
environmental science and engineering, while working in the lab of Yuk
L. Yung, Caltech professor of planetary science and research scientist
at the Jet Propulsion Laboratory, which Caltech manages for NASA. She
found that methane concentrations in the air above L.A. fluctuate in
tandem with the seasons. In winter, when natural gas use is at its
highest, methane concentrations are also highest. In the summer, when
natural gas use drops, so does the amount of methane in the air.
"Naturally, methane emissions should be pretty flat across the seasons,
but maybe a little higher in the summer period because of a lot of
things decompose from higher temperatures," He says. "But it seems that
in the city, natural gas consumption is so high in the winter that a lot
of it leaks into the atmosphere."
He conducted her research by using a device called a remote-sensing
spectrometer atop Mt. Wilson, a mountain whose peak towers a mile above
Los Angeles. From its lofty perch, the spectrometer had a view of a wide
swath of the urban area below. Methane is invisible to human eyes, but
it is easily seen by the spectrometer because it strongly absorbs
infrared light, the wavelength of light to which the spectrometer is
sensitive.
Using this setup, the spectrometer was pointed at 33 surface sites
around the region and collected methane measurements six to eight times
a day for six years. When those measurements were aggregated, a clear
pattern emerged: methane levels in the atmosphere peaked each December
and January and dipped to a low each June and July.
Though He's research does not identify specific sources of methane, she
says that it is likely that the entire natural gas distribution system,
from storage fields to pipelines to stoves and furnaces, is responsible
for the leaks.
Because methane is such a potent greenhouse gas, and because it is
relatively short-lived in the atmosphere, identifying and reducing those
natural gas leaks is one way humans might help reduce the effects of
climate change, He says.
"Agriculture and wetlands are still the most important sources of
methane when we consider the global scale, He says. "But I think
pipeline leakage is the most important one when it comes to cities."
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