Fine and Ultrafine Particle Emissions and Dynamics in the Burn Zone Following the 2025 Los Angeles Fires
HAOXUAN CHEN, Qiyue Nie, Jing Li, Yuan Yao, Qiao Yu, Muchuan Niu, Vine Blankenship, Haroula D. Baliaka, Richard Flagan, Nga Lee Ng, Roya Bahreini, Ann M. Dillner, Armistead G. Russell, Yifang Zhu, University of California, Los Angeles
Abstract Number: 428
Working Group: Burning Questions of Aerosol Emissions, Chemistry, and Impacts from Wildland-Urban Interface (WUI) Fires
Abstract
The increasing wildland-urban interface (WUI) fires pose complex challenges for air quality and public health due to their distinct aerosol emission characteristics. Even after full containment, WUI fire zones may continue to impact local air quality through persistent emissions from smoldering debris, ash resuspension, and post-fire cleanup or rebuilding activities. Yet, the characteristics and dynamics of fine aerosols in these post-fire environments remain poorly understood.
Following the full containment of the Eaton Fire, we conducted mobile and stationary aerosol measurements in the burn zone over multiple days during Phase 1: Hazardous Material Removal in February and Phase 2: Debris Removal in March of the Emergency Response. An electric vehicle platform equipped with multiple real-time aerosol instruments—including a condensation particle counter, DustTrak aerosol monitor, scanning mobility particle sizer, and aerodynamic particle sizer—was deployed to monitor particle concentrations and PM2.5 mass concentrations, as well as particle size distributions spanning 13 nm to 20 μm.
Compared to measurements at the ASCENT (Atmospheric Science and Chemistry mEasurement NeTwork) Pico Rivera site which is located approximately 20 km away, we observed distinct patterns of fine aerosol emissions and dynamics in the burn zone. Particle concentrations more frequently exceeded 1×104 particles/cm3, with a dominant mode between 10–30 nm, suggesting primary aerosol emissions. Evidence of particle growth was also observed, likely driven by secondary formation mechanisms from abundant semi-volatile organic compounds. In addition, a submicron particle mode (0.5–1 μm) was frequently detected and associated with elevated PM2.5 levels.
These findings highlight the complex and evolving nature of post-fire aerosol pollution in WUI fire zones, with implications for community exposure during ongoing cleanup and rebuilding activities. Our results underscore the importance of continued monitoring to better characterize exposure risks and inform post-fire air quality management strategies.