Methane Emissions in Los Angeles Higher Than Previously Thought

Yearly methane emissions in Los Angeles are higher than previously thought, according to a new NASA study.

Methane is an extremely potent greenhouse gas, and 20 percent more efficient at trapping heat in our atmosphere than the more infamous carbon dioxide. And based on a novel mountaintop instrument called a spectrometer, which essentially "counts" the number of methane molecules in the air, annual emissions are 18 to 61 percent higher than widely used estimates.

"For the first time, we've been able to provide an accurate estimate of total methane emissions from the Los Angeles basin, whatever their sources," senior research scientist Stanley Sander, of NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement. "Altogether, it's a very significant increase in the estimate."

Normally scientists calculate how much methane is in the atmosphere in any given place by adding up estimated emissions from all known methane sources, such as pipeline leaks, landfills, wastewater treatment plants and transportation. But in this case, the spectrometer, part of the California Laboratory for Atmospheric Remote Sensing (CLARS), acts as a stationary satellite. From its position high atop Mt. Wilson some 5,700 feet (1,700 meters) above Los Angeles, the novelty instrument surveys over 28 flat, unobstructed sites throughout the Los Angeles basin during the day, measuring how much methane, carbon dioxide and other pollutants are in the air between it and each site.

It also takes a measurement in the clean air above the mountain, the difference being the amount of methane in the sprawling 30-by-70-mile LA basin (50 by 110 kilometers).

In total, methane emissions were estimated to be a whopping 430,000 tons per year - that's way more than previous estimates had indicated.

So where is all this methane coming from exactly?

"The ones we have been able to identify are - perhaps coincidentally, but perhaps not - located near large landfills. That is consistent with our understanding that landfills have the potential to be methane sources under certain conditions," Sander explained.

It really comes at no surprise to scientists the significant amount of methane spewing into the atmosphere from Los Angeles, considering that cities are some of the biggest emitters - 70 percent of the world's carbon emissions come from urban areas.

Human-related sources, such as livestock, landfills and leaks of natural gas, are largely to blame for the buildup of this heat-trapping gas. Researchers hope to put CLARS-like instruments in other huge cities that are overlooked by mountains one day, such as Rio de Janeiro, Seoul and Mexico City.

The results were published in the journal Atmospheric Chemistry and Physics.

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