Key takeaways
- Air quality downwind of the fires saw sharp, immediate increases in harmful pollutants — most notably airborne lead, which surged up to 250 times above normal baseline levels during active burning.
- Smoke and heavy metals cleared from the air, returning to normal background levels, within roughly six days after the flames were extinguished.
- Even after the fires were largely controlled in the urban areas and burning moved to the wildlands, the smoke contained elements thought to be from urban burning.
A new study from UCLA provides critical insights into how the January 2025 Eaton fire impacted air quality downwind of the fires, highlighting how levels of airborne toxic contaminants spiked and then dissipated as the burning died down.
The study found that during active burning, the smoke carried extremely elevated levels of lead, arsenic, chlorine, bromine and copper. Additionally, researchers found no evidence that toxic smoke or heavy metals lingered in the air after the fires were put out, with air pollution levels returning to normal within six days and remaining so for months after.
"As wildland-urban interface fires like what the LA region experienced in January 2025 become more frequent, this study helps us better understand the immediate risks posed by smoke from these kinds of fires to surrounding communities," said Suzanne Paulson, professor of atmospheric and oceanic sciences and one of the study's authors. She is also director of UCLA's Center for Clean Air, housed in the Institute of the Environment and Sustainability.
"Still, there's more work to be done to better understand the dynamics of how burning in urban environments versus wildlands affects the makeup of the pollutants in the smoke these fires produce," Paulson said.
To understand how smoke and dust traveled downwind through local neighborhoods, researchers combined air quality data from two monitoring locations downwind of the Eaton fire — one at UCLA's campus and one at the South Coast Air Quality Management District's Huntington Park Station, about 17 miles south-southwest of the fire's start — with satellite fire tracking and wind models. This allowed the team to separate fire smoke data from everyday city emissions.
The study also found that the exact source of the contaminants — whether from burning wildlands or urban buildings — couldn't be clearly separated.
"Elements like lead, arsenic, zinc, bromine and chlorine are expected to be higher in smoke from urban fires, but we found that they persisted even when the fires shifted away from the urban areas and into the wildlands," said Catherine Banach, a UCLA Ph.D. student researcher and co-author of the study.
"And potassium, which is usually used as a marker of burning vegetation, didn't correlate to increased smoke levels, but rather to dust particles kicked up by the winds," she said. "This drives home the complexity of these kinds of fires and the need for a better understanding of the area's soils before using these indicators to assume the sources of their emissions."
