HR: 08:55h
AN: A41E-04    [Abstracts]
TI: Aerosol Mass Scattering Efficiency: Generalized Treatment of the Organic Fraction
AU: * Garland, R M
EM: rebecca.garland@colorado.edu
AF: Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309 United States
AU: * Garland, R M
EM: rebecca.garland@colorado.edu
AF: CIRES, UCB 216, University of Colorado, Boulder, CO 80309 United States
AU: Ravishankara, A R
EM: A.R.Ravishankara@noaa.gov
AF: Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309 United States
AU: Ravishankara, A R
EM: A.R.Ravishankara@noaa.gov
AF: Aeronomy Laboratory, NOAA, Boulder, CO 80303 United States
AU: Lovejoy, E R
EM: nlovejoy@al.noaa.gov
AF: Aeronomy Laboratory, NOAA, Boulder, CO 80303 United States
AU: Tolbert, M A
EM: margaret.tolbert@colorado.edu
AF: Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309 United States
AU: Tolbert, M A
EM: margaret.tolbert@colorado.edu
AF: CIRES, UCB 216, University of Colorado, Boulder, CO 80309 United States
AU: Baynard, T
EM: tbaynard@al.noaa.gov
AF: CIRES, UCB 216, University of Colorado, Boulder, CO 80309 United States
AU: Baynard, T
EM: tbaynard@al.noaa.gov
AF: Aeronomy Laboratory, NOAA, Boulder, CO 80303 United States
AB: Atmospheric aerosols are complex mixtures of organic and inorganic compounds. Current efforts to provide a simplified parameterization to describe the RH dependence of water uptake and associated optical properties lack the capability to include any dependence on the composition of the organic fraction. Using laboratory generated aerosol we have investigated the validity of such simplified treatment of organic fraction and estimated potential biases. In this study, we use cavity ring-down aerosol extinction photometry (CRD-AEP) to study the relative humidity (RH) dependence of the light extinction of aerosols, σ_ep, simultaneously considering the influence of particle size, chemical composition, and mixing state (internal and external mixtures). We have produced internally mixed aerosol systems including; ammonium sulfate, ammonium nitrate, sodium chloride, dicarboxylic acids, sugars, amino acids and humic acid. These aerosols are produced with an atomizer and size-selected with a Differential Mobility Analyzer (DMA). The particles then enter into a CRD-AEP to measure dry extinction, σ_ep(Dry), after which they travel into a RH conditioner and another CRD-AEP to measure the humidified aerosol extinction, f_σ(ep)RH. The ratio of the humidified extinction to the dry extinction is f_σ(ep)RH. Representative organic compounds were found to have f_σ(ep)RH values that are much smaller than pure salts; though the f_σ(ep)RH values vary little within the organic compounds studied. In addition, we have found that treating the inorganic/organic aerosols as external mixtures is generally correct to within ~10%, indicating appropriate simplified treatment of the RH dependence of atmospheric aerosol according to inorganic/organic fraction. In this presentation, we include recommendations for the generalized treatment of the organic fraction, exceptions to this generalized behavior, and estimates of the potential bias caused by generalized treatment.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0365 Troposphere: composition and chemistry
DE: 1610 Atmosphere (0315, 0325)
DE: 3337 Global climate models (1626, 4928)
DE: 3394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005