AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Role of Aerosol Water in Secondary Organic Aerosol Formation from Volatile Organic Compounds
JENNIFER FAUST, Jenny Wong, Alex K. Y. Lee, Jonathan Abbatt, University of Toronto, Canada
Abstract Number: 301 Working Group: Aerosol Chemistry
Abstract 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. Secondary organic aerosol (SOA) can form when volatile organic compounds (VOCs) are oxidized to yield semivolatile species, which then condense onto atmospheric seed particles and partition into the aqueous phase according to physical solubility. Most commonly, dissolution is driven by processes like hydration; other reactions within the condensed phase also enhance overall uptake.
Here we report SOA yields from the oxidation of isoprene, toluene, and alpha-pinene on deliquesced and effloresced ammonium sulfate seeds within a room-temperature oxidation flow tube held at 70% relative humidity. In the case of isoprene photooxidation by OH, we find a strong 60% enhancement in SOA formation on deliquesced relative to effloresced seeds. Particle acidity does not affect SOA yield from isoprene but does generate more highly oxidized products with greater molecular weights, likely due to acid-catalyzed reactions and oligomerization. Both toluene photooxidation by OH and alpha-pinene oxidation by ozone exhibit weak enhancements in SOA yield on wet relative to dry ammonium sulfate seeds. Preliminary results further suggest that SOA formation from alpha-pinene ozonolysis is initially driven by condensation of extremely low volatility organic compounds (ELVOCs), in contrast to the isoprene and toluene systems, which are dominated by semivolatile species. Overall, we conclude that particle-phase water mediates SOA formation in the atmosphere, but the extent of its influence varies widely among VOC precursors.