Using a new detection method, UC Riverside scientists have found a massive amount of methane, a super-potent greenhouse gas, coming from wildfires—a source that is not currently being accounted for by state air quality managers.
Methane is heating the planet 86 times more strongly than carbon dioxide over a 20-year period, the researchers said, and it would be difficult for the country to reach its required goals for clean air and climate without accounting for this source.
Wildfires emitting methane are nothing new. But the amount of methane from 20 fires in 2020 was more than seven times the average for wildfires in the past 19 years, according to the new UCR study.
“The fires are getting larger and more intense, so more emissions are coming from them,” said Francesca Hopkins, UCLA professor of environmental sciences and co-author of the study. “The fires in 2020 emitted what would have been 14 percent of the state’s methane budget if tracked.”
The state does not track natural sources of methane, such as those that come from wildfires. But for 2020, wildfires were the third largest source of methane in the state.
“Usually, these sources have been hard to measure, and it’s questionable whether they are under our control. But we have to try,” Hopkins said. “They make up for what we’re trying to cut back on.”
Traditionally, scientists measure emissions by analyzing wildfire air samples obtained via aircraft. This ancient method is expensive and complicated to propagate. To measure emissions from the 2020 Sequoia Lightning Fire complex in the Sierra Nevada, the UCLA research team used remote sensing technology, which is safer for scientists and potentially more accurate because it captures an integrated column of fire that includes different burning stages.
Technology, Hinge in the journal Atmospheric chemistry and physics, lead author, PhD in Environmental Sciences UCR. Student Isis Frausto-Vicencio to safely measure an entire plume of gas and debris from the Sequoia Lightning Fire complex from 40 miles away.
“The plume, or atmospheric plume, is like a mixed signal for the entire fire, capturing both the active as well as the burning phases,” Hopkins said. “This makes these measurements unique.”
Instead of using a laser, as some devices do, this technology uses the sun as a source of light. Gases in the plume absorb and then emit the sun’s thermal energy, allowing insights into how much aerosols as well as carbon and methane are present.
Using remote control technology, the researchers found nearly 20 gigagrams of methane emitted from the Sequoia Lightning Fire complex. One gigagram equals 1000 metric tons. An elephant weighs about a metric ton. For context, the fire thus contained approximately 20,000 elephants of gas.
This data matches measurements that came from European Space Agency satellite data, which took a more comprehensive global view of burned areas, but is not yet able to measure methane in these conditions.
If included in the California Air Resources Board’s methane budget, wildfires would be a greater source than residential and commercial buildings, power generation, or transportation, but beyond agriculture and industry. While 2020 was exceptional in terms of methane emissions, scientists expect more years of wildfires going forward with climate change.
In 2015, the state first set a goal to reduce methane, refrigerants, and other air pollutants by 40 percent by 2030. The following year, in 2016, Governor Jerry Brown signed SB 1383, codifying those reduction goals into law.
The cuts are meant to come from regulations that capture methane produced from manure on dairy farms, eliminate food waste in landfills, require oil and gas producers to reduce leaks, ban certain gases in new refrigerators and air conditioners, and other measures.
“California has moved forward on this issue,” Hopkins said. “We really hope that the country can reduce methane emissions under our control to reduce short-term global warming and its worst effects, despite the additional emissions coming from these fires.”
Isis Frausto-Vicencio et al, Earth-Sun absorption observations of total column CO, CO, CH, and aerosol optical depth from the Sequoia Lightning Complex fire in California: emission factors and combustion efficiency adjusted at regional scales, Atmospheric chemistry and physics (2023). DOI: 10.5194/acp-23-4521-2023
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