Using a new detection method, UC Riverside scientists found a massive amount of methane, a super-potent greenhouse gas, coming from wildfires—a source not currently being accounted for by state air quality managers.
Methane warms the planet 86 times more powerfully than carbon dioxide over the course of 20 years, and it will be difficult for the state to reach its required cleaner air and climate goals without accounting for this source, the researchers said.
Wildfires emitting methane is not new. But the amount of methane from the top 20 fires in 2020 was more than seven times the average from wildfires in the previous 19 years, according to the new UCR study.
“Fires are getting bigger and more intense, and correspondingly, more emissions are coming from them,” said UCR environmental sciences professor and study co-author Francesca Hopkins. “The fires in 2020 emitted what would have been 14 percent of the state’s methane budget if it was being tracked.”
The state does not track natural sources of methane, like those that come from wildfires. But for 2020, wildfires would have been the third biggest source of methane in the state.
“Typically, these sources have been hard to measure, and it’s questionable whether they’re under our control. But we have to try,” Hopkins said. “They’re offsetting what we’re trying to reduce.”
Traditionally, scientists measure emissions by analyzing wildfire air samples obtained via aircraft. This older method is costly and complicated to deploy. To measure emissions from 2020’s Sequoia Lightning Fire Complex in the Sierra Nevadas, the UCR research team used a remote sensing technique, which is both safer for scientists and likely more accurate since it captures an integrated plume from the fire that includes different burning phases.
The technique, detailed in the journal Atmospheric Chemistry and Physics, allowed the lead author, UCR environmental sciences Ph.D. student Isis Frausto-Vicencio to safely measure an entire plume of the Sequoia Lightning Fire Complex gas and debris from 40 miles away.
“The plume, or atmospheric column, is like a mixed signal of the whole fire, capturing the active as well as the smoldering phases,” Hopkins said. “That makes these measurements unique.”
More information: Isis Frausto-Vicencio et al, Ground solar absorption observations of total column CO, CO2, CH4, and aerosol o.ptical depth from California’s Sequoia Lightning Complex Fire: emission factors and modified combustion efficiency at regional scales, Atmospheric Chemistry and Physics (2023). DOI: 10.5194/acp-23-4521-2023.
Journal information: Atmospheric Chemistry and Physics.
Provided by University of California – Riverside.