This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A new study from UCLA provides insights into how the January 2025 Eaton fire affected air quality downwind, showing how levels of toxic airborne contaminants spiked and then dissipated as the burning died down. The research is published in the journal ACS ES&T Air.
The study found that during active burning, the smoke carried extremely elevated levels of lead, arsenic, chlorine, bromine and copper. Researchers found no evidence that toxic smoke or heavy metals lingered in the air after the fires were put out. Air pollution levels returned to normal within six days and remained there for months.
"As wildland-urban interface fires like what the Los Angeles 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, a 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 on UCLA's campus and one at the South Coast Air Quality Management District's Huntington Park Station, about 17 miles (27 kilometers) south-southwest of where the fire started—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 burning wildlands or urban buildings—couldn't be clearly determined.
"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." Catherine A.
Banach et al, Air Quality during and after the 2025 Los Angeles, California Fires and the Utility of Potassium as a Fire Tracer, ACS ES&T Air (2026). DOI: 10.1021/acsestair.6c00085 Provided by University of California, Los Angeles MA in English, copy editor since 2021 with experience in higher education and health content. Dedicated to trustworthy science news.
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