Decoding clues on dominant combustion phase and aerosol chemical regimes via key tracers of fire plumes

Wildfire events have increased in severity in recent years, contributing to environmental changes and posing risks to Air Quality (AQ) and public health. Evaluating their chemical composition is critical for mitigating the impacts of biomass burning. In this study, thirteen fire events, sampled during the 2019 FIREX-AQ field campaign in the US, were evaluated. The aircraft in-situ data with fuel type assessments revealed the dominance of flaming combustion, with modified combustion efficiency values exceeding 0.9. The abundance of light-absorbing carbonaceous species (LACS) was investigated alongside correlations between gas and particle-phase emissions, identifying potential indicators of the dominant in-plume organic aerosol (OA) chemical regimes. The majority of the examined plumes were classified as aged. Their composition reflected a balance between OA oxidation-driven condensation and dilution-driven evaporation, with dilution-driven evaporation emerging as the prevailing chemical process. The evaluation of combustion phase and dominant chemical regimes of OA via main fire tracers and LACS underscore the importance of these species to plume characteristics and evolution.