Methane above Los Angeles higher than expected

Methane, the second-most potent of the greenhouse gases, is produced and emitted at higher levels in the Los Angeles Basin than previously estimated, according to a new study by scientists at NASA’s Jet Propulsion Laboratory.

The gas is a by-product of decomposition, so a lot of local emissions come from moldering garbage in landfills. Leaky pipelines and car exhaust also contribute to the area’s emissions.

Scientists say that methane emissions from megacities, such as Los Angeles, can have global impacts.

“In order to understand how climate is changing, we need to have this very broad view of the concentrations of methane, how they’re distributed in space and in time,” said Stan Sander, a senior research scientist at NASA’s Jet Propulsion Laboratory.

The Los Angeles Basin has 18 percent to 61 percent more methane than previous estimates report. Sander said that the wide variation in the calculation represents uncertainty in measuring actual amounts of methane and that further refinement would narrow the gap.

The currently accepted method for calculating methane emissions is to tally up estimates of emissions from known sources.

The new data come from a spectrometer stationed in the San Gabriel Mountains as part of the Mount Wilson Observatory. It overlooks the basin and measures the amount of methane filtering through reflected sunlight.

Sander said that the technology will be shared with other cities. Within 10 years, he expects a spectrometer will be installed on a satellite to monitor planet-wide emissions.

“It’s very important to address the global question, because methane is a long-lived gas. It survives in the atmosphere for many years,” Sander said.

Sander said the study identified hotspots for methane production with the Los Angeles basin. One of them was in East Los Angeles; the other, in Pasadena near the Rose Bowl. Both have landfills located within the hotspot, though Sander said it isn’t clear how much methane those sources contribute.