Higher reactivity of biomass burning aerosols in generating the OH burst when encountering clouds

Hydroxyl radical (OH)-mediated cloud water chemistry impacts air quality and climate directly and indirectly by modifying aerosol mass concentration, chemical composition, and size distribution. Here, we investigate the ability of particles to produce an ‘OH burst’ - the period of rapid OH formation that takes place when particles first take up water to form cloud droplets. We explore the underlying factors influencing the OH burst through field campaigns at the Department of Energy Southern Great Plains (DOE-SGP) site, using a Direct-to-Reagent spot sampler, during spring and late summer 2022. We analyze particle composition, including biomass burning organic aerosol, semi-volatile and low-volatile oxidized organic aerosol, and several inorganic species based on the Aerosol Chemical Speciation Monitor (ACSM) measurement and Positive Matrix Factorization (PMF) analysis. Furthermore, we develop a novel approach to estimate the cloud processing history of collected ambient particles by combining the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and ECMWF ERA5 reanalysis data. We investigate the associations between the OH burst and various chemical species and cloud processing indicators, and further apply a multivariate regression model to predict the OH burst. Our results indicate biomass burning aerosols exhibit significantly higher reactivity to generate OH burst when interacting with clouds. This discovery points to a potentially significant role of the OH burst in aerosol oxidation and aging processes, with implications for their broader climate impact, which warrants further investigation.