Two peer-reviewed studies led by UCLA researchers have documented the severe air quality impacts of recent California wildfires, revealing how dangerous smoke particles spread across communities and highlighting gaps in current monitoring systems.
The studies, published by UCLA Fielding School of Public Health researchers, examined both the devastating January 2025 Los Angeles County fires and the major 2018 blazes across California, providing crucial insights into wildfire smoke exposure as fire seasons continue to lengthen across the western United States.
The January fires in Pacific Palisades-Malibu and Altadena-Pasadena claimed at least 31 lives and damaged or destroyed more than 18,000 structures, according to county estimates. The blazes also sent dangerous airborne particles spreading across the Los Angeles basin, affecting air quality for millions of residents.
"Wildfires can degrade air quality in downwind communities," said Dr. Miriam Marlier, assistant professor in UCLA Fielding's Department of Environmental Health Sciences and a co-author of both studies. "By integrating data from multiple sources — ground monitors, atmospheric models, and satellites — our research aims to provide a more complete picture of smoke exposure during wildfire events."
Both studies focused on PM2.5, dangerous particles less than 2.5 micrometers in diameter — 30 times smaller than a human hair. These microscopic particles pose serious health risks because of their ability to penetrate deep into lungs and enter the bloodstream.
"Because these particles are so small, they can travel deep into your lungs and even enter your bloodstream — potentially leading to serious problems like heart or lung disease," said Dr. Michael Jerrett, professor in UCLA Fielding's Department of Environmental Health Sciences and co-director of the UCLA Center for Healthy Climate Solutions. "For anyone, exposure to fine particles can contribute to health issues, and for those with existing conditions or heightened sensitivity, the risks are even greater."
The 2025 Los Angeles County study, published in Environmental Science & Technology Letters, compared three air quality monitoring methods: federal monitoring stations, low-cost sensors and satellite imagery. Each data source showed distinct advantages and limitations.
Federal monitors provided highly accurate data but exist in limited numbers. Low-cost sensors are less accurate but more widespread. Satellite imagery covers larger areas but does not always reflect ground-level conditions.
"Timely and accurate air quality information is crucial for the public to reduce their smoke exposure during wildfire events," said Dr. Claire Schollaert, the study's lead author and a UCLA Fielding postdoctoral research scientist. "Combining federal monitors, low-cost sensors, and satellite data can provide a more complete picture of local air quality, which can help people make safer choices in real time."
The research showed smoke plumes traveled downwind and affected large portions of the LA basin, though the extent varied dramatically from day to day and neighborhood to neighborhood as fires progressed and wind patterns shifted.
The companion study of 2018 California fires, published in Environmental Science & Technology Air, found that the 10 largest fires that year accounted for nearly all detected fire-derived PM2.5 pollution. The team used atmospheric modeling with satellite-based wildfire emissions inventories to separate wildfire contributions from other pollution sources.
"The largest 2018 wildfires were responsible for the vast majority of downwind fire-derived PM2.5 concentrations in the locations that we examined in California," Marlier said.
However, researchers noted significant gaps remain in current monitoring capabilities, particularly for urban wildfires.
"During and after wildfires, people want to know whether it's safe to go outside or take their kid to school or the playground," said Dr. Lara Cushing, associate professor in the UCLA Fielding Department of Environmental Health Sciences. "We can't currently answer those questions thoroughly because existing air quality monitoring networks do not measure all pollutants of concern — including heavy metals and air toxics that are released when buildings and cars are burned in urban wildfires — and we lack data about the persistence of pollutants in indoor spaces that were exposed to smoke and ash."
The research teams included scientists from UCLA, UC Merced and the University of British Columbia. Members are currently seeking public participation in an ongoing study examining public health impacts after the 2025 fires.
The studies received funding from the National Science Foundation, California Air Resources Board, University of California Multicampus Research Program and Initiatives, and the Gordon and Betty Moore Foundation.