Real-Time Trace Element Insights from ASCENT During the 2025 Los Angeles Urban Wildfires

HAROULA D. BALIAKA, Ryan Ward, Sean Raffuse, Can Barut, Armistead G. Russell, Bradley Ries, Yumeng Cui, Roya Bahreini, Eleanor Bentley, Lelia Hawkins, David Hagan, John Seinfeld, Paul Wennberg, Richard Flagan, Nga Lee Ng, California Institute of Technology

     Abstract Number: 580
     Working Group: Burning Questions of Aerosol Emissions, Chemistry, and Impacts from Wildland-Urban Interface (WUI) Fires

Abstract
Urban wildfires are an emerging air quality threat across the western United States, and real-time chemical composition data of urban fire plumes are vital for evaluating health impacts. The Eaton Canyon (Altadena) and Palisades firestorms in Los Angeles, which ignited in January 2025, led to widespread combustion of synthetic materials, raising concerns about the toxicity of the fine particulate matter. Real-time, high-resolution measurements from the Los Angeles Atmospheric Science and Chemistry mEasurement NeTwork (ASCENT) site in Pico Rivera (14 miles downwind of Altadena) captured the plume, during which certain elements exhibited enrichment ratios far above background levels, with sharp spikes observed for Cl, Br, and certain metals such as Pb. Positive Matrix Factorization (EPA PMF v5.0) source apportionment was applied to disentangle background levels from fire-related enhancements and to identify distinct chemical fingerprints associated with the combustion of urban materials. To assess regional impacts, we integrated data from Caltech and additional ASCENT sites in Rubidoux, Riverside, and Joshua Tree into a spatial modeling framework.