File:Declining Methane Emissions in the Los Angeles Basin (PIA25863).tiff

A February 2023 study by researchers at NASA's Jet Propulsion Laboratory in Southern California analyzed data on atmospheric methane concentrations from ground-based sensors scattered around four densely populated Southern California counties. It found that emissions of the powerful greenhouse gas methane fell by about 7% between 2015 and 2020 – a reduction of 33 million pounds (15 million kilograms) of methane released per year.

This bar graph shows that overall emissions in the study area decreased between 2015 and 2019, the last full year of the data for the study. Error bars indicate uncertainties in the estimates for each year.

Published in Environmental Research Letters, the paper is based on measurements from eight spectroscopic sensors that were installed as part of the Megacities Carbon Project, a multiagency collaboration monitoring greenhouse gases in the Los Angeles, Indianapolis, and Washington, D.C., areas. The sensors have been gathering data since 2015. The California data enabled researchers to study an area that stretches from the beaches of Malibu in the west to the mountains and deserts of San Bernardino and Riverside counties in the east. It also extends south through all of Orange County.

The researchers found that the month-to-month fluctuations in methane concentrations around Los Angeles gradually fell from 2015 to 2020, and well into 2022 – a strong indication that local emissions of the gas were also decreasing. Then, using a mathematical model to estimate the emissions decrease, they found the areas covered by sensors in Granada Hills (Los Angeles County) and Ontario (San Bernardino County) accounted for much of the drop in annual emissions from 2015 to 2020.

Although the paper doesn't cite causes of the emission reductions in those two locales, researchers suspect they resulted from better management of natural gas pipelines and equipment, which in turn led to lower fugitive – or accidental – methane releases. Improved infrastructure at a massive landfill near Granada Hills likely also played a role.