By Ahmed Abdelsalam
Smoke from the 2025 Los Angeles fires exposed approximately 7 million residents to airborne lead concentrations 80 times higher than normal background levels during a 24-hour peak period, according to a study published Wednesday in the journal Science Advances.
Devastating 2025 Los Angeles fires
The two wind-driven fires in Altadena and Pacific Palisades ignited on Jan. 7, 2025, killing at least 31 people and destroying more than 16,000 structures, mostly homes. Thousands of burned structures released toxic chemicals from cars, paint, furniture, and household chemicals.
Urban fire smoke differs fundamentally from wildfire smoke
Researchers from the California Institute of Technology compared smoke from the Eaton Fire with a 2024 vegetation fire in Riverside County. The urban plume contained 50 times more lead, three times more arsenic, and seven times more halogens such as chlorine and bromine, linked to burning vehicles, building materials, and electronics. Nga Lee “Sally” Ng, a study author, said the findings show wildfire smoke is fundamentally different from urban smoke.
Real-time measurements reveal detailed chemical composition
The study used the Atmospheric Science and Chemistry mEasurement NeTwork (ASCENT), a new U.S. network of air quality monitors that measures particulate size and chemical composition hourly. This allowed researchers to track how smoke composition changed and distinguish emissions from burning structures. Co-author Haroula Baliaka said understanding these differences fills a research gap.
Health risks from short-term heavy metal exposure
Lead is a neurotoxin that can impair children’s development and increase blood pressure in adults, while arsenic exposure is linked to cancers. Scientists do not yet know the health effects of short-term, high-level lead exposure. Ed Avol, a professor emeritus at the University of Southern California, called the documented exposure levels surprising and noted the study’s hour-by-hour measurements are a significant advance over typical weekly sampling.
Experts call for adapted monitoring and policy
Yaguang Wei of the Icahn School of Medicine at Mount Sinai said the findings reinforce that wildfire smoke particulates are more toxic than other sources and have important policy implications. He recommended stronger public health protections, increased wildfire monitoring, and more prescribed fires. Avol emphasized the need to protect people from toxic materials in homes as urban and wildland areas increasingly intersect.
