Metals in Wind-Dispersible Dust and Ashes During and After the 2025 Los Angeles Fires

JING LI, Yuan Yao, Haoxuan Chen, Qiao Yu, Priscilla Boo, Yifang Zhu, University of California, Los Angeles

     Abstract Number: 147
     Working Group: Burning Questions of Aerosol Emissions, Chemistry, and Impacts from Wildland-Urban Interface (WUI) Fires

Abstract
The 2025 Los Angeles (LA) wildfires, which began on January 7 and were contained by January 31, ranked among the most destructive in California’s history. These fires were notable for their proximity to densely populated Wildland-Urban Interface (WUI) areas. The Palisades Fire and Eaton Fire together destroyed 18,000 structures, potentially releasing large amounts of metals into the environment. Few studies have characterized the metal content in wind-dispersible dust and ashes. We collected 70 dust and ash samples from the areas surrounding the Palisades and Eaton fires in LA County over three periods: January (January 14-25, n = 32), February (February 10-11, n = 14), and March (March 9, 10, and 27, n = 24). All samples were collected using anti-static brushes onto weighing papers from surfaces such as mailboxes, windowsills, benches, and tables. We measured concentrations of 16 metals including lead (Pb), cadmium (Cd), and chromium (Cr) in these samples in ng/mg (ppm). Preliminary results showed that, taking Pb as an example, 8/33 samples from Eaton and 4/37 samples from Palisades exceeded the EPA screening level for Pb in soil (200 ppm). Samples from different periods showed significantly different Pb concentrations, with February (98 [47] ng/mg, median [IQR]) > January (51 [174] ng/mg) > March (49 [75] ng/mg) (ANOVA on Ranks, p = 0.033). Samples from the area impacted by the Eaton Fire (mostly Altadena and Pasadena communities, n = 33) had significantly higher concentrations than those from the Palisades Fire (mostly Pacific Palisades and Malibu communities, n = 37) (Mann-Whitney Rank Sum Test, p = 0.034), with the former at 74 [163] ng/mg and the latter at 47 [62] ng/mg. Ongoing analysis will explore spatial and temporal trends in other metals to better understand potential risks attributed to WUI fires on human and environmental health.