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Greenhouse Gases

Roughly 50 sites generate one-third of California methane emissions

Landfills produce much of that methane, followed by dairies and oil and gas operations

by Jeff Johnson, special to C&EN
November 12, 2019

Photo of a bulldozer in a garbage-filled landfill.
Credit: Mark Rightmire/ZUMA Press/Newscom
Landfills are "super emitters" of methane in California.

A small number of methane emitters generate a disproportionate amount of California’s methane emissions and landfills are the biggest culprit, according to a study examining greenhouse gas emissions in the state.

The study determined that some 50 point-source methane emitters—defined as individually identifiable sources of methane—generate more than half of the state’s point-source methane emissions and one-third of the state’s overall methane emissions (Nature 2019, DOI: 10.1038/s41586-019-1720-3).

The key point-source methane emitters in California are oil and natural gas fields, large dairies, and landfills. Nonpoint sources include, for example, natural gas leaks from homes that by themselves are small, although they may collectively add up to a large amount.

Over a 2-year period, a research team at the NASA Jet Propulsion Laboratory flew a plane equipped with infrared imaging instrumentation over nearly 300,000 facilities in California and identified 564 individual point sources emitting high concentrations of methane.

When examined closely, the researchers found only 10% of those high emitters emitted 60% of measured methane emission. They further determined that methane point-source emissions in California are dominated by landfills (41%), followed by dairies (26%) and the oil and gas sector (26%).

Finding that a small number of “super emitters” generate a comparatively large amount of methane matches similar aerial studies conducted over a broader swath of the US; however, those examinations usually identified oil and gas drilling and production to be primary emitters, rather than landfills.



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