AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Organic Matrix Effects on Aqueous Processing in Atmospheric Aerosols
GREG DROZD, V. Faye McNeill, Columbia University
Abstract Number: 762 Working Group: Aerosol Chemistry
Abstract The aqueous processing of organic compounds in atmospheric particles affects important particle properties, such as hygroscopicity and absorption of light. The chemical environment in particles that have deliquesced but have not yet effloresced is quite unique, with necessarily supersaturated salt concentrations. Recent studies on phase separations in atmospheric particles indicate that water soluble organic material (WSOC) that is highly oxidized (O:C > 0.7) remains in a single phase with ammonium sulfate and water.(1) This organic matrix has the potential to make the particle system differ greatly from a bulk solution in several ways (e.g. viscosity, dielectric constant,etc.). In this work we probe the effect of organic matrices on the reaction of glyoxal and methylglyoxal with ammonium sulfate, using highly soluble organics to serve as surrogates for WSOC. We find that at an organic to sulfate mass ratio of 2 to 1, glucose reduces the rate of product formation by 30%. Methanol and ethanol have pH dependent effects on reaction rates. Reduced conductivity in solutions with an organic matrix suggests lower charge carrier density due to increased ion pairing in the highly concentrated solution. The reduced ammonium activity due to ion pairing contributes to the observed reduction in reaction rate. Organic matrices may affect the rate of aqueous processing and hence the formation of light absorbing or hygroscopicity altering compounds, particularly in conditions that are common inside or near clouds, which will result in changes in cloud properties, such as brightness and lifetime.
1. Bertram et al., Atm. Chem Phys., 11, 10995, 2011.