Using a mix of airborne and satellite images as well as data from ground sensors, a UCLA-led research team has reconstructed how the shape and reach of the methane plumes from the 2015–16 Aliso Canyon gas blowout evolved during the 112-day disaster.
Starting from the beginning of the disaster in October and up until the end of the disaster in February, methane plumes from the Aliso Canyon gas storage facility likely reached at least 6.2 miles downwind from the blowout site into the nearby Porter Ranch neighborhood in northwestern Los Angeles County.
The study also confirmed earlier estimates of total emissions of nearly 100,000 metric tons of methane during the blowout, which is equivalent to 20% of all of California's annual methane emissions and double the typical methane emission rate for the Los Angeles Basin.
BACKGROUND
The Aliso Canyon disaster began Oct. 23, 2015, and lasted until Feb. 11, 2016. The UCLA-led Aliso Canyon Disaster Health Research Study team and partners have been working to assess the short- and long-term health effects of the gas blowout, the largest uncontrolled release of toxic air pollutants from an underground gas storage facility in U.S. history.
Before properly investigating those health effects, the researchers needed to determine how far from the blowout site the emissions reached and how the distance from the Aliso Canyon facility affected the amount of potential exposure. Determining the reach and intensity of the methane plumes allows the researchers to get a more informed estimate of how many people were potentially affected.
METHOD
The research team reviewed cloud-free images of the site captured by the Landsat-8 and Sentinel-2 satellites to see where methane was present in the atmosphere early in the blowout event and how far it moved from the source into the nearby areas.
Then they used additional images collected later during the blowout — some from the Hyperion satellite and others from an Airborne Visible/Infrared Imaging Spectrometer (AVIRIS), which was flown on an airplane.
The final data sets came from the California Air Resources Board's ground monitors in the Aliso community. The two monitors collected hourly methane concentrations from December 2015 through March 2016. Researchers collected the hourly methane concentrations for the dates and times that aligned with clear-sky remote sensing images to connect and quantify correlation between satellite and ground-based observations.
IMPACT
The study's findings form an essential foundation for the Aliso Canyon Disaster Health Research Study team's work to investigate the health effects of the blowout. Without knowing how far into the surrounding neighborhoods the methane plumes reached, it would be more difficult to understand who might have been affected by the blowout.
The results also demonstrated the usefulness of using remote sensing data to characterize potential exposures from similar disasters.
The authors note that leveraging multiple satellite and airborne remote sensing platforms and connecting it with data they had on the ground provided valuable footing for the team to better understand the size, shape and intensity of the methane gas released from the event.
AUTHORS
The lead author is Daniel Cusworth, director of science at Carbon Mapper and a UCLA Aliso Canyon Disaster Health Research Study team partner. The study was co-led and co-authored by Miriam Marlier, assistant professor of environmental health sciences at the UCLA Fielding School of Public Health. Other UCLA authors are Michael Jerrett, professor of environmental health sciences at the Fielding School of Public Health and principal investigator of the UCLA Aliso Canyon Disaster Health Research Study; and Aron Walker and Sydney Monte-Sano of the department of environmental health sciences at the Fielding School. Massimo Stafoggia, of the department of epidemiology in the regional health service of Lazio in Rome, Italy, was also an author.
JOURNAL
The study was published in the journal Environmental Research Communications.
FUNDING
In November 2022, the Los Angeles County Department of Public Health awarded a UCLA-led research team a five-year contract of approximately $21 million to assess the short- and long-term health effects of the gas blowout.
