Lead in the Air During the January 2025 Los Angeles Fires

By Haroula D. Baliaka, Ryan X. Ward, Roya Bahreini, Ann M. Dillner, Armistead G. Russell, John H. Seinfeld, Richard C. Flagan, Paul O. Wennberg and Nga L. Ng — California Institute of Technology, University of California Riverside, University of California Davis and Georgia Institute of Technology

At a glance

• Known: smoke is a complex mix of gases and particles, and urban fires give off different pollutants from ordinary wildfires. ASCENT, a new air-quality network, measures the chemistry of fine particles (PM2.5) in real time.
• New: during the January 2025 Los Angeles fires, ASCENT recorded lead in PM2.5 about 110 times higher than in the days before.
• So what: urban fire smoke carries different risks, and health studies should consider what PM2.5 is made of. Health officials should tell the public how to protect themselves: watch air quality forecasts, and follow emergency officials' guidance.

When cities burn

On January 7, 2025, the Eaton Canyon and Palisades fires swept across the Los Angeles region, driven by exceptionally dry conditions and Santa Ana gusts approaching 100 mph (161 kph). They spread into dense neighborhoods at the wildland-urban interface, destroying about 16,000 structures; 29 deaths had been identified by February 10, 2025.

Wildfire PM2.5 — particles smaller than 2.5 μm — degrades air far downwind and is linked to more asthma, respiratory symptoms, worse lung disease and higher death rates (1–3). But these fires burned the built environment: paint, pipes, vehicles, plastics, electronics and buildings. Many of the structures predated 1978, when leaded paint was still common — raising concern about what the smoke contained.

The measurements

ASCENT (the Atmospheric Science and Chemistry mEasurement NeTwork), funded by the National Science Foundation, continuously measures PM2.5's organics, inorganics, metals and black carbon at 12 U.S. sites — seven urban and five remote or rural, including Great Smoky Mountains, Joshua Tree and Yellowstone national parks. All were running by May 2024.

The Los Angeles site, in Pico Rivera, about 14 miles (23 km) south of the Eaton Canyon fire, has operated since July 2023. During and after the fires, southward winds carried the plume over it.

Hourly PM2.5 lead at the Los Angeles ASCENT site, January 2025. CDC.

For comparison, during the 2018 Camp fire, lead in PM2.5 averaged 0.13 μg/m³ over 17 hours (2). Lead in urban fire smoke is not unusual, especially in California, where old infrastructure, industry and soils hold legacy pollutants that fires can release (2,4).

What it means

Lead is toxic. It spreads through the body's tissues, builds up in teeth and bones, and affects nearly every organ system — especially in children, whose developing brains are most vulnerable (2,3,5).

• The long decline: since the Clean Air Act of 1970, airborne lead has fallen sharply; taking lead out of gasoline, pipes and products such as house paint has cut it by 97% since 1980 (5).
• The standard: the national air-quality standard for lead is 0.15 μg/m³, averaged over 3 months.
• The unknown: long-term lead exposure is well studied; short, high bursts like this one are not. And airborne levels alone don't show how much people actually took in — more health research is needed.

PM2.5 is a changing mix of chemicals and particle sizes. Its health effects are well documented, but which sources, chemicals and sizes matter most is not. Real-time chemical data like ASCENT's, combined with health data, can help answer that — for these fires and beyond.

Sources

Based on Haroula D. Baliaka, Ryan X. Ward, Roya Bahreini, Ann M. Dillner, Armistead G. Russell, John H. Seinfeld, Richard C. Flagan, Paul O. Wennberg and Nga L. Ng, "Notes from the Field: Elevated Atmospheric Lead Levels During the Los Angeles Urban Fires — California, January 2025," MMWR, Centers for Disease Control and Prevention; a work of the United States government in the public domain. Numbers in parentheses refer to the report's references.