Multimodal Approach for Assessing Emissions and Transport of Greenhouse Gases and Air Pollutants from the January 2025 Los Angeles Wildfires

Wildfires are an increasingly dominant source of greenhouse gases and criteria air pollutants in urbanized regions. Continuing to refine quantifications of the atmospheric impacts of urban wildfires is an important goal to improve predictions of future events relevant to both the global carbon budget and public exposure. Here, we analyze the January 2025 Los Angeles (LA) wildfires by integrating satellite imaging, meteorological models, advection and diffusion models, and dense ground-level air quality observations from both low-cost sensors and reference-grade instruments. Focusing specifically on the Eaton fire, we demonstrate how its emissions were transported across LA, noting the rate of spread and the magnitude of pollutant enhancements achieved. We complement our measurements with bottom-up estimates of the carbon content lost from the fires and corroborate our approach through a Gaussian dispersion plume analysis. Our analyses indicate that the Eaton fire consisted of two distinct periods of burning which differentially consumed structures and vegetation, and our bottom-up budget and atmospheric observations agree that the combustion of structures released significantly more carbon than that of vegetation. During the period of most intense burning, emission rates of CO (CO2) were estimated to be approximately 21.2–37.6× (0.9–1.2×) greater than average daily anthropogenic contributions. Subsequent observational evidence of pollutant concentrations also highlights the outsized contribution of wildfire CO emissions, relative to normal conditions. The impact of wildfire emissions on fine particulate matter is then assessed through the lens of both primary emissions and potential secondary formation. Additionally, we note how spikes in methane concentrations point to wildfire-driven destruction of natural gas infrastructure. Together, these results demonstrate the value of our multimodal approach in elucidating a holistic picture of the consequences of urban wildfires with respect to public health and greenhouse gas emissions.