PM Exposure Associated With Burned Buildings During the Los Angeles Wildfires in 2025

MICHAEL KLEEMAN, Sean Raffuse, David T. Allen, Yosuke Kimura, Colette Schissel, University of California, Davis

     Abstract Number: 286
     Working Group: Burning Questions of Aerosol Emissions, Chemistry, and Impacts from Wildland-Urban Interface (WUI) Fires

Abstract
The wildfires that occurred in Los Angeles during January 2025 were among the most destructive in the history of California. Approximately 57,000 acres burned, consuming more than 18,000 structures and resulting in 30 deaths. The urban nature of the fire generated significant concentrations of toxic compounds in the wildfire smoke, including lead, arsenic, and halogenated compounds associated with burned metals, plastics, and other building materials. The ash and soil within and around the wildfire zones was also enriched in toxic compounds, raising the possibility that debris removal and cleanup over a period of months could expose the ~18M nearby residents of Los Angeles to further levels of toxic air pollution. This presentation will predict air pollution exposures during both the active burning phase and cleanup phase of the wildfire using a source-oriented chemical transport model (CTM). During the burning phase, the spatial distribution of fire emissions were based on detailed, high resolution inventories of structures, structure contents and vegetation. The temporal evolution of the burned area was based on satellite observations. Emissions from specific regions and burn times were tracked. The fire emissions are combined with other air pollution emissions to predict how the emissions age in the atmosphere. During the cleanup phase, measured size and composition distributions of dust generated in the burned zone will be used to model deposition rates for different toxic compounds contained in the PM. The ability of the CTM to reproduce measured PM concentrations during and after the wildfire event will be evaluated. Tagging features within the CTM will be used to quantify wildfire contributions to ambient PM separated from other sources. Wildfire contributions to ultrafine, fine, and coarse particle PM will be discussed. Finally, population exposure and relative risk associated with burning natural vegetation vs. burning buildings will be presented.