AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Formation of Hydrogen Peroxide and Hydroxyl Radicals by Ambient Particles in Simulated Cloud Water
Xiaobi Kuang, John Scott, David Gonzalez, SUZANNE PAULSON, University of California Los Angeles
Abstract Number: 220 Working Group: There Must be Something in the Water: Cloud, Fog and Aerosol Aqueous Chemistry for Aerosol Production
Abstract Aerosol aging plays an important role in modifying aerosol chemical composition, hygroscopicity, cloud condensation nuclei activity and optical properties. Aqueous phase aerosol aging is mediated by reactive oxygen species (ROS), which include hydroxyl radicals (OH), hydrogen peroxide (H2O2), superoxide anion (O2.-) and organic peroxides. Similar oxidation processes in cloud water may provide a pathway for secondary organic aerosol (SOA) formation through cloud processing during nighttime. Two field campaigns were carried out in summer in Claremont, CA, a receptor site in the Los Angeles air basin, and in winter in Fresno, CA, a site with substantial influence from residential biomass burning aerosol. The resulting samples were extracted in an atmospherically relevant solution (water at pH3.5), and analyzed for particle mass, steady-state H2O2 concentration and OH generation, speciated soluble iron, and total soluble trace metals. Soluble iron was about 50% Fe(II) and 50% Fe(III) in the Claremont samples but was shifted slightly in favor of Fe(II) in the Fresno samples (66%). On a per-mass basis, the Fresno PM produced similar steady-state H2O2 concentrations, and while morning and afternoon Fresno samples generated similar OH as the Claremont PM, overnight samples produced much more OH. H2O2 was poorly correlated with aerosol mass, but strongly correlated with soluble iron and manganese at both sites. OH formation was strongly correlated to Cu, Fe and aerosol mass for the Claremont samples. Further, samples that had experienced more aging (6-hour back trajectories were largely aloft) had higher H2O2, OH and soluble iron compared to those with less aging (6-hour back trajectories were predominantly along the surface). OH formation was most strongly related to biomass burning aerosols in the Fresno samples, and was otherwise low.