Particulate Matter Composition and Sources in the Urban-Wildland Interface After the 2025 Southern California Wildfire
CHUN-YING CHAO, Albert Kyi, Katarina Konon, Shihao Zhai, Chou-Hsien Lin, Evelyn Deveraux, Anna Neville, Daniel Sung, Pawel K. Misztal, David T. Allen, Lea Hildebrandt Ruiz, University of Texas at Austin
Abstract Number: 108
Working Group: Burning Questions of Aerosol Emissions, Chemistry, and Impacts from Wildland-Urban Interface (WUI) Fires
Abstract
The 2025 wildland-urban interface (WUI) wildfire in Southern California (Eaton and Palisades Fire) burned over 37,000 acres and destroyed more than 15,000 homes and structures. The WUI wildfire extended into suburban and urban neighborhoods and resulted in complex pollutants from combustion fueled by vegetation, buildings, and vehicles. The impact of WUI wildfire residuals, such as ash and burned houses, on aerosol loading and chemical composition is still unclear.
To better understand the post-impact of WUI wildfire across Los Angeles County, this study (1) investigates the spatiotemporal chemical characteristics of aerosol and (2) identifies the source of organic aerosol (OA) using positive matrix factor (PMF). We deployed an Aerodyne high-resolution time-of-flight aerosol mass spectrometer in the mobile air quality lab to investigate in-situ aerosol composition after the WUI wildfire in Los Angeles from February 3 to 24. Mobile measurements were conducted in fire-affected neighborhoods with varying levels of impact, and indoor and outdoor stationary sampling was conducted in selected homes with different degrees of wildfire damage. In addition to the HR-ToF-AMS, a Vocus proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS), a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), an aethalometer, and a Toxic-Metal Aerosol Real-Time Analysis (TARTA) were deployed in the same mobile platform to comprehensively measure the impact of WUI wildfire.
PMF analysis identified five OA factors: hydrocarbon-like OA (HOA), less-oxygenated OA (LO-OOA), more-oxygenated OA (MO-OOA), cooking OA (COA), and nitrogen-containing OA (NOA). In previous studies, the NOA factor was found to be associated with combustion activities. Its mass spectrum profile showed substantial contributions of CO2+ signal (m/z 44), suggesting that this factor could be attributed to secondary OA (SOA) formation from wildfire combustion. The results indicate that the residual of WUI wildfire may potentially serve as a persistent post-fire source of SOA and impact long-term air quality.