Institutional development · Research, innovation and assessment · United States
Caltech finds Eaton Fire smoke held over 50 times the lead found in wildfire smoke
Caltech researchers report that smoke from the January 2025 Eaton Fire in Altadena was chemically distinct from ordinary wildfire smoke, carrying far higher levels of lead, arsenic, chlorine and bromine.
Why it matters: Researchers studying air quality and health during urban fires now have measured toxic-metal data from Caltech's analysis of the Eaton Fire plume.
Caltech researchers say they have produced the first detailed study of airborne particles in smoke from the Eaton Fire, which destroyed much of Altadena in California's San Gabriel Valley in January 2025.
A monitoring station downwind recorded toxic metal levels rising sharply in the fire's early phase, when buildings and vehicles were alight, with the chemical profile shifting once flames reached the mountains of the Angeles National Forest, Caltech reported.
Compared with smoke from a typical wildfire, lead in the urban plume was more than 50 times higher, chlorine and bromine roughly seven times higher and arsenic about three times higher, according to the team.
The scientists estimate that when structural burning peaked, close to 7 million people across metropolitan Los Angeles breathed lead at 24-hour concentrations 80 times above usual levels.
Editor’s view
Scott James, Research and Innovation Editor
Caltech said the findings could inform modelling work, and the team's estimate places close to 7 million Los Angeles-area residents among those exposed to elevated lead at the fire's peak.
