Fire at the boundary: Airborne toxic metals from the 2025 Los Angeles urban firestorm
Urban fire smoke is chemically distinct from wildland fire smoke yet remains poorly understood. Using real-time airborne trace element measurements during the 2025 Los Angeles Eaton urban firestorm, we show that the plume evolved rapidly as fire transitioned from structures to wildland, tracked hourly by the potassium-to-lead ratio. Compared to wildfire smoke, the urban plume was enriched more than 50-fold in lead, 7-fold in halogens, and 3-fold in arsenic, a toxic mixture linked to burning vehicles, electronics, and building materials, a fundamentally different fuel from conventional wildland vegetation. During peak structural burning, we estimate that approximately 7 million residents (range, 4.3 to 8.0 million) experienced 24-hour lead concentrations exceeding 50 nanograms per cubic meter, over 80 times background levels. Unlike wildfire smoke that has been the focus of decades of air quality research, this plume represents an emerging class of urban fire air pollution that demands revised exposure frameworks and emergency response protocols as fires increasingly burn into cities.
Authors
- John H. Seinfeld (ORCID: https://orcid.org/0000-0003-1344-4068)
- Yumeng Cui (ORCID: https://orcid.org/0000-0003-2945-7381)
- Dien Wu (ORCID: https://orcid.org/0000-0002-2915-5335)
- Richard C. Flagan (ORCID: https://orcid.org/0000-0001-5690-770X)
- François L. H. Tissot (ORCID: https://orcid.org/0000-0001-6622-2907)
- Sean M. Raffuse (ORCID: https://orcid.org/0009-0000-1026-282X)
- R. Bahreini (ORCID: https://orcid.org/0000-0001-8292-5338)
- N. L. Ng (ORCID: https://orcid.org/0000-0001-8460-4765)
- Ryan X. Ward (ORCID: https://orcid.org/0000-0003-2317-3310)
- Haroula D. Baliaka (ORCID: https://orcid.org/0000-0001-7851-8449)
- Paul O. Wennberg (ORCID: https://orcid.org/0000-0002-6126-3854)
- Armistead Goode Russell (ORCID: https://orcid.org/0000-0003-2027-8870)
- Sina Hasheminassab (ORCID: https://orcid.org/0000-0002-4422-8547)
- B. Ries (ORCID: https://orcid.org/0009-0000-4454-477X)
- Can Barut (ORCID: https://orcid.org/0009-0009-8849-1521)
- Ruizhe Liu (ORCID: https://orcid.org/0009-0009-5582-5046)
Institutions
- University of California, Riverside (US)
- California Institute of Technology (US)
- Georgia Institute of Technology (US)
- Jet Propulsion Laboratory (US)
- University of California, Davis (US)
- Colorado State University (US)
Publication Details
- Journal
- Science Advances
- Published
- 2026-10-28
- DOI
- https://doi.org/10.1126/sciadv.aei4455
- Primary Topic
- Atmospheric chemistry and aerosols
- Type
- article
- Field-Weighted Citation Impact
- 0.00
Funders
- National Science Foundation
- California Institute of Technology
- Resnick Sustainability Institute for Science, Energy and Sustainability, California Institute of Technology
- Alexander S. Onassis Public Benefit Foundation
- Jet Propulsion Laboratory