Investigating Uncertainties in Air Pollutant Emissions of Structure and Biomass Burning from the 2025 Los Angeles Fires

Abstract

The January 2025 wildland–urban interface (WUI) fires in Los Angeles (LA) County significantly affected regional air quality. Here, using the best available fuel loading data sets, emission factor (EF) measurements, and satellite fire products, we develop a high-resolution, spatiotemporally resolved emissions inventory of structure burning for the LA fires. Our results reveal substantial uncertainties in estimated structure burning emissions, driven by variability in EFs, building damage fractions, and combustible mass loading. We also incorporate building composition (e.g., wood and other materials) when estimating structure burning emissions and find that accounting for building composition changes emission estimates. Our uncertainty quantification analysis indicates larger uncertainties for NOX and CO emissions and smaller uncertainties for PM2.5 emissions. We further compare biomass burning emissions across five commonly used inventories and find large variability among inventories, with differences reaching up to a factor of 73 depending on pollutant and fire event. These findings highlight the need for improved building composition, damage, and EF data to reduce uncertainties in WUI fire emission estimates. Emission inventories in this study could be used in air quality models to investigate the air quality impacts and associated uncertainties of the LA fires.