California gas leak spewed massive amounts of methane

The months-long natural gas leak from a well in California’s San Fernando Valley released 97,100 metric tons of methane and 7,300 metric tons of ethane into the air above Los Angeles, researchers estimate February 25 in Science. For the first six weeks of the leak, the well spewed at most 59 metric tons of methane and 4.4 metric tons of ethane per hour — twice the normal emission rate of the entire Los Angeles Basin, the researchers say.

The leak began in October in one of the wells at the Aliso Canyon oil storage facility. After many attempts to plug the leaky pipe, workers finally sealed it on February 18.

To assess the impact of the leak on local air quality, Stephen Conley of the University of California-Davis and his colleagues assessed the impact of the leak collected downwind air samples on the ground and from above — via 13 flights aboard a small aircraft over three months of the leak.

Methane and ethane both increase atmospheric ozone levels and, at high levels, impact human health. Los Angeles is home to many small natural gas leaks as well, another group reports February 20 in the Journal of Geophysical Research: Atmospheres. Mapping methane release across the basin prior to the blowout revealed 213 hotspots of unknown origin. Such maps could also give researchers a clearer sense of the impact of the blowout on Los Angeles methane emissions.