AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Kinetics and Products of Multiphase Aging Reactions of Organic Aerosol
JESSE KROLL, James Hunter, Kelly Daumit, Sean Kessler, Anthony Carrasquillo, Eben Cross, Theodora Nah, Douglas Worsnop, Kevin Wilson, MIT
Abstract Number: 583 Working Group: Aerosol Chemistry
Abstract Atmospheric organic aerosol (OA) tends to be substantially higher in mass loading and carbon oxidation state than OA produced in laboratory studies. Further, oxidized OA is produced on timescales on the order of one day in the atmosphere, significantly faster than has been achieved in the laboratory. This suggests major gaps in our understanding of the chemistry underlying OA formation and evolution, and has led to several suggested multiphase mechanisms for the rapid generation of high yields of highly oxidized OA. Here we present a series of laboratory studies of the formation and aging of oxidized organic aerosol, focusing on both the particulate reaction products (abundance and average oxidation state of particulate organic carbon), and the rate at which such products are formed. Oxidative “aging” of secondary organic aerosol mixtures (in which gas-phase reaction products are exposed to sustained concentrations of hydroxyl radicals) is found to lead to increases in both particle mass and degree of oxidation, but over timescales substantially longer than a day for the mixtures studied. Heterogeneous oxidation of a wide range of particulate organics is similarly found to be too slow to account for observations of oxidized OA formation. Aqueous-phase chemistry also provides a pathway for the formation of highly oxidized organics, but first requires that organics partition into the condensed phase prior to being oxidized, and so can also be quite slow under atmospheric conditions. Consideration of both kinetics and partitioning together is needed to predict potential channels for the rapid formation of highly oxidized, low-volatility organics.