The Atmospheric Science and Chemistry mEasurement NeTwork (ASCENT)† is a new, nationwide, multi-institutional initiative funded by the National Science Foundation, to provide continuous measurements of PM2.5 chemical components (organics, inorganics, metals, and black carbon) across 12 sites in the United States, including seven urban and five remote or rural areas.§ All ASCENT sites were operating and sampling ambient air as of May 2024.
The Los Angeles ASCENT site in Pico Rivera, approximately 14 miles (23 kilometers) south of the Eaton Canyon fire, has been operating since July 2023. During and immediately after the Los Angeles fires, southward winds transported the fire plume to the ASCENT site. Hourly PM2.5 lead measurements recorded during and after the fires were reviewed to assess their contribution to atmospheric lead levels. Because this analysis consists of a review of routinely collected environmental data and does not include human subjects, human subjects review was not required by the authors’ institutions.
During January 2–6, 2025, the average PM2.5 lead concentration recorded at the Los Angeles ASCENT site was 0.00068 μg/m3. From January 8 to January 11, PM2.5 lead concentration increased approximately 110 times with an average concentration of 0.077 μg/m3 (Figure). Recorded PM2.5 lead concentration peaked at approximately 0.5 μg/m3 on January 9. By the evening of January 11, PM2.5 lead concentration had returned to levels similar to those before the fire. The presence of heavy metals such as lead is not unusual in urban fire emissions, particularly in California, where legacy pollutants from older infrastructure, industrial sources, and soils can be remobilized during fires (2,4). For example, during the 2018 Camp fire, monitors recorded ambient PM2.5 lead concentrations that averaged 0.13 μg/m3 during a period of 17 hours (2).
Few data illustrate the health effects of lead from inhalation compared with other exposure routes. The ASCENT real-time measurements of airborne lead and other chemical constituents in PM2.5 provide valuable PM2.5 chemical composition data that can be combined with health data to examine health effects of individual smoke components from the Los Angeles fires.