Abstract
The modification of cloud condensation nucleus (CCN) activity of saturated organic particles resulting from heterogeneous oxidation by OH radicals was studied. Submicron Bis-2-ethylhexyl sebacate (BES) and stearic acid particles were exposed to OH radicals in a reactor flow tube and CCN activity was monitored. The hygroscopicity parameter, κ, for monodisperse stearic acid and BES particles of 145–150 nm in size increased from <0.008 up to 0.08 as a result of OH exposures equivalent to atmospheric exposure timescales of several days to a week. The oxidation of stearic acid particles led to a 50% reduction in particle volume at high OH exposures, indicating an enhanced degree of volatilization of oxidation products compared to oxidized BES particles, along with possible shape/phase change. Surface tension measurements of water extracts of oxidized BES films showed a significant reduction in surface tension due to oxidation. Köhler calculations modeling the CCN measurements suggest that the surface active oxidation products play an important role.
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