Public data reveal extent of air quality impacts during 2025 Los Angeles wildfires

(Press-News.org) In early 2025, wildfires spread in Los Angeles, destroying tens of thousands of homes and businesses. During the fires, smoke blanketed the region and online maps provided residents with rapid air quality information. Now, a study in ACS’ Environmental Science & Technology Letters compares the data that went into the maps from federal monitoring stations, low-cost sensors and satellites. Their results highlight the importance of combining multiple data sources to form easily accessible information for the public.

“Timely and accurate air quality information is crucial for the public to reduce their smoke exposure during wildfire events,” says Claire Schollaert, the study’s corresponding author. “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.”

Wildfires create smoke and haze that can be harmful to breathe. To reduce smoke exposure and mitigate potential health risks, public health experts recommend checking the local Air Quality Index (AQI) before stepping outside. The AQI ranks outdoor air from “Good” to “Hazardous,” calculating values from the levels of air pollutants present, including fine particulate matter (PM2.5). The U.S. Environmental Protection Agency’s (EPA) AirNow Fire and Smoke Map and the PurpleAir low-cost sensor network are online platforms that provide AQI information from ground monitors. Additionally, the AirNow Fire and Smoke Map provides smoke plumes from the National Oceanic and Atmospheric Administration’s (NOAA) Hazard Mapping System. Satellite observations of near-real time air pollution are also collected but aren’t readily available on these popular online platforms. In a retrospective of the January 2025 LA wildfires, Schollaert and colleagues compared the data provided in these three publicly available datasets to understand where overlaps and informational gaps may occur.

The researchers obtained air quality monitoring data for LA County from eight EPA stations in the AirNow network, 728 low-cost particulate matter sensors, and satellite data of smoke plume outlines and pollutant concentrations. During the fire period, when the Eaton and Palisades wildfires ignited and intensified (Jan. 7-12, 2025):

EPA stations detected elevated PM2.5 levels in downtown LA and Compton, reaching “Unhealthy” and “Unhealthy for Sensitive Groups” AQI categories, respectively. Twelve of the low-cost sensors located closer to the fires (within 4.7 miles, 7.5 kilometers) had PM2.5 levels in the “Hazardous” AQI range. Satellite images tracked the movement of light- to heavy-density smoke in the atmosphere, which generally matched places on the ground with elevated PM2.5 levels. The stationary ground monitors showed that high AQI values generally aligned with the locations of thick smoke plumes seen by the satellites, though this was not always the case. Additionally, each data source has its advantages and disadvantages: The EPA monitors are highly accurate but limited in number, the low-cost sensors are less accurate but more prolific, and the satellites cover even more ground but don’t always reflect the conditions on the ground. But combined, these tools could be useful for people in smoke-impacted areas to make informed decisions about their exposure risks in near real time, the researchers say.

The authors acknowledge funding from the Gordon and Betty Moore Foundation and Climate and Wildfire Research Initiative at the University of California, Los Angeles.

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