Hundreds of methane-emitting hot spots have been identified across the Los Angeles Basin, including a "clean ports" truck refueling facility near the Port of Long Beach, power plants, water treatment facilities, and cattle in Chino, according to new findings by the University of California, Irvine. Atmospheric scientists conducted a mobile survey across Los Angeles, Orange and Riverside counties, and their results, published this week in the Journal of Geophysical Research: Atmospheres, identify the region's highest emitters. Methane is the second-largest known contributor to global climate change, behind carbon dioxide.

The survey was done before the Aliso Canyon gas well leak temporarily displaced thousands from their Porter Ranch homes. The findings could be used by the Southern California Gas Co. to meet orders by Gov. Jerry Brown and the state Air Resources Board to offset the gas leak by removing as much of the fast-acting greenhouse gas from the air as was emitted from the Aliso Canyon site, the researchers said.

Lead author Francesca Hopkins said the survey "identified numerous methane hot spots that could be targets for these mitigation activities."

The researchers drove a specially equipped cargo van for hundreds of miles throughout the Los Angeles region, taking readings with instruments designed to measure methane, ethane, carbon monoxide and carbon dioxide. They observed heightened methane levels across the basin and pinpointed 213 hot spots.

"Our surveys demonstrate the prevalence of unwanted methane emissions across the Los Angeles urban landscape and show that two-thirds of the gas comes from fossil fuel origins," said Hopkins, who began the work as a postdoctoral scholar at UCI. "Known sources of methane include cattle, geologic seeps, landfills and compressed natural gas fueling stations."