AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
The Salty World of Aqueous Aerosols: Biogenic OVOC Partitioning over the South Eastern US
RAINER VOLKAMER, Eleanor Waxman, Neha Sareen, Paul Ziemann, Elm Jonas, Theo Kurten, Annmarie Carlton, University of Colorado
Abstract Number: 351 Working Group: The Role of Water in Aerosol Chemistry
Abstract Recent field observations suggest that aerosol sulfate (SO$_4$^(2-)) directly controls a significant fraction of secondary organic aerosol (SOA) mass over biogenic environments such as the South Eastern US. Setschenow salting-constants, K$_S, describe the exponential dependence of the gas- / aqueous phase partitioning (Henry’s Law constant) on the salt concentration. Knowledge about K$_S is of particular importance to predict SOA formation in aerosol water, where the salt concentrations are typically very high. Such salt-induced activity is not typically captured by activity coefficients, and can modify SOA formation rates by altering (1) the effective Henry’s Law partitioning coefficient (by several orders of magnitude), (2) changing the multiphase chemical reaction rates; and (3) the volatility of products through the formation of complexes and/or organo-sulfate/nitrate products. This talk discusses laboratory measurements combined with quantum calculations to better understand the values of K$_S for biogenic OVOC, such as glyoxal, methyl glyoxal and isoprene epoxide in a range of atmospherically relevant salts, incl. (NH$_4)$_2SO$_4, NH$_4NO$_3, NaNO$_3 and NaCl. We find that glyoxal ‘salts-in’ (negative K$_S) consistently, while methyl glyoxal ‘salts-out’. The Gibbs Energy of the chemical bonds of glyoxal, methyl glyoxal and isoprene epoxide with SO$_4$^(2-), NO$_3$^-, and Cl$^- is compared, and used to interrogate their salting-behavior. Our best estimates of K$_S values for glyoxal, methyl glyoxal and isoprene epoxide have been incorporated into the CMAQ model, and a range of simulations were conducted to predict the effect of salts on their partitioning and potential to form SOA over the continental US.