AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Implications of Aerosol-phase Photocatalytic Epoxidation and Ion-specific Enhancement of Organic Partitioning
GE YU, Frank Keutsch, University of Wisconsin - Madison
Abstract Number: 413 Working Group: Aerosol Chemistry
Abstract Organosulfates have been proposed as an important contributor to organic aerosol mass. It has been demonstrated that organosulfates can be formed in aerosol via reaction of epoxides with sulfate, highlighting the importance of understanding mechanisms of epoxide formation. We present a new pathway for epoxide formation via catalytic, photo-sensitized oxidation of alkenes in aerosol by molecular oxygen in the presence of alpha-dicarbonyls. We report the reaction kinetics and reaction products for different alkenes, as well as yields, which can reach 100% in 30 minutes of solar exposure. The high rate constants determined in our experiments as well as high alpha-dicarbonyl concentration in organic aerosol mass estimated by a statistical model suggest that this reaction may limit the lifetime of alkenes in the organic phase. The formation of epoxides has implications for not only organosulfate formation but also the production of other aerosol components, such as polyalcohols and organonitrates, and increases hygroscopicity of pure organic phase particles.
In addition to the formation of organosulfates, inorganic sulfate may influence organic aerosol mass and composition by modifying the partitioning of organic compounds between the gas and aqueous phases. It has recently been demonstrated that the Henry’s law coefficient of glyoxal is dramatically increased by as low as millimolar sulfate concentrations, and underlying physicochemical mechanisms have been proposed to account for this effect. We extend this previous work to other organic species to determine for which types of organics this effect is active and how important this effect may be, e.g., for anthropogenic (sulfate) influence on rural secondary organic aerosol formation.