HR: 0800h
AN: A21E-0799    [Abstracts]
TI: Uptake and Reactions of Formaldehyde, Acetaldehyde, Acetone, Propanal and Ethanol in Sulfuric Acid solutions at 200-240 K: Implications for upper tropospheric aerosol composition
AU: * Iraci, L T
EM: Laura.T.Iraci@nasa.gov
AF: Atmospheric Science Branch, MS 245-5 NASA - Ames Research Center, Moffett Field, CA 94035, United States
AU: Williams, M B
EM: mbwilliams@arc.nasa.gov
AF: Atmospheric Science Branch, MS 245-5 NASA - Ames Research Center, Moffett Field, CA 94035, United States
AU: Williams, M B
EM: mbwilliams@arc.nasa.gov
AF: Bay Area Environmental Research Institute, 560 Third St. W, Sonoma, CA 95476, United States
AU: Axson, J
EM: Jessica.Axson@Colorado.edu
AF: Atmospheric Science Branch, MS 245-5 NASA - Ames Research Center, Moffett Field, CA 94035, United States
AU: Michelsen, R
EM: rmichelsen@rmc.edu
AF: Department of Chemistry, Randolph Macon College, Ashland, VA 23005, United States
AB: The production of light absorbing, organic material in aerosol that is normally considered to be transparent in the UV and visible wavelength regions has significant implications for biogeochemical cycling and climate modelling. Production mechanisms likely involve carbonyl compounds such as formaldehyde, acetone, acetaldehyde and propanal that are present in significant quantities in the upper troposphere (UT). In this study, we have performed experiments focusing on a class of acid catalyzed carbonyl reactions, the formation of acetals. R₂C=O + 2R'OH --> R₂C(OR')₂ + H₂O Using a Knudsen cell apparatus, we have measured the rate of uptake of formaldehyde, acetaldehyde, acetone, propanal, and ethanol into sulfuric acid solutions ranging between 40-70 wt% of acid, containing 0-0.1 M of ethanol, acetone or formaldehyde at temperatures of 220-250 K. For all reactant pairs, the aldol condensation path, including self reaction, should be insignificant at the acidities studied. Evidence for reaction between organics was observed for all pairs, except those involving propanal which were likely limited by the very low solubility. We attribute enhanced uptake to the formation of acetals, such as 1,1-diethoxyethane and 2,2- diethoxypropane, among others. Enhanced uptake was observed to proceed on timescales > 1 hour and sometimes shows complex dependence on acidity that is likely related to speciation of the individual carbonyls in acidic solution. The acetal products do not absorb in the visible but are less volatile than parent molecules, allowing for accumulation in sulfuric acid particles, and enhanced uptake. Cross reactions of carbonyls with alcohols in sulfuric acid medium have not been previously measured, yet methanol and ethanol show high solubility and are present at significant concentrations in the UT. Thus even at slow reaction rates, the acetal reaction has ample starting material and proceeds under conditions common to the UT. We will present results for the enhanced uptake of carbonyls in the presence of alcohols, derive rate constants, and discuss the atmospheric impact of the acetal reaction path.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0365 Troposphere: composition and chemistry
DE: 0490 Trace gases
DE: 1610 Atmosphere (0315, 0325)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting