Aerosol droplets present a unique aqueous reaction medium in the atmosphere because of their small volume and high concentrations of both inorganic and organic solutes. One mechanism governing secondary organic aerosol (SOA) formation occurs when photooxidation of gas-phase organic compounds yields semivolatile, water-soluble species, which then condense onto atmospheric seed particles. These oxidation products partition into aqueous aerosols according to their physical solubility; most commonly, dissolution is driven by processes like hydration, but reactions within the condensed phase can also enhance overall uptake. Here we report SOA yields from the photooxidation of a variety of VOC precursors on wet and dry ammonium sulfate seeds within a room-temperature oxidation flow tube held at 70% relative humidity. We have found a strong 60% enhancement in SOA formation on deliquesced seed particles relative to effloresced seeds in the case of isoprene. Particle acidity did not affect SOA yield but did lead to more highly oxidized products with higher molecular weights, likely due to acid-catalyzed reactions and oligomerization. To test the general influence of aqueous-phase chemistry on SOA formation, we extend the isoprene studies to two additional SOA precursors, toluene and a-pinene.

Role of aerosol water in secondary organic aerosol formation from volatile organic compounds

251st National Meeting (2016)

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