OH Burst Measurement: Online Direct-to-Reagent System to Measure OH Formation by Cloud Processed Ambient Aerosols

The OH radical mediated cloud water chemistry has impacts on both direct and indirect effects on the climate and contributes to the processing of aerosols (e.g. size distributions and chemical composition). Previously the gas-phase uptake of OH was thought to be the dominant source of OH in cloud droplets. However, recent work shows an aqueous phase process in which particles grown into nascent cloud droplets produce a significant ‘OH burst’ on order and even larger than the gas phase uptake. The magnitude of the ‘burst’ is dependent on chemical composition but also on the degree of cloud processing the particles undergo. In this study we utilize a direct-to-reagent method in which particles are continually captured and grown into cloud droplets then deposited into solution to measure OH formation. OH Measurements were made at the Scripps Mt. Soledad site during the Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) campaign to determine how cloud processing affects the ability of a particle to generate OH. We further investigate the influence of particle chemical composition and size distribution by pairing our data to onsite measurements made with the Aerodyne Mass Spectrometer (AMS).