Atmos. Chem. Phys. Discuss., 7, 3589-3627, 2007
www.atmos-chem-phys-discuss.net/7/3589/2007/
doi:10.5194/acpd-7-3589-2007
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Investigation of molar volume and surfactant characteristics of water-soluble organic compounds in biomass burning aerosol
A. Asa-Awuku1, A. Nenes1,2, A. P. Sullivan2,*, C. J. Hennigan2, and R. J. Weber2
1School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA
2School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
*now at: Department of Atmospheric Sciences, Colorado State University, Fort Collins, CO, USA

Abstract. In this study, we characterize the CCN activity of the water-soluble organics in biomass burning aerosol. The aerosol after collection upon filters is dissolved in water using sonication. Hydrophobic and hydrophilic components are fractionated from a portion of the original sample using solid phase extraction, and subsequently desalted. The surface tension and CCN activity of these different samples are measured with a KSV CAM 200 goniometer and a DMT Streamwise Thermal Gradient CCN Counter, respectively. The measurements show that the strongest surfactants are isolated in the hydrophobic fraction, while the hydrophilics exhibit negligible surface tension depression. The presence of salts (primarily (NH4)2SO4) in the hydrophobic fraction substantially enhances surface tension depression; their synergistic effects considerably enhance CCN activity, exceeding that of pure (NH4)2SO4. For our analysis, average thermodynamic properties (i.e., molar volume) are determined for samples using our newly developed K√∂hler Theory Analysis (KTA) method. We have found that, the molar mass of the hydrophilic and hydrophobic aerosol components is estimated to be 87±26 g mol−1 and 780±231 g mol−1, respectively. KTA also suggests that the relative proportion (in moles) of hydrophobic to hydrophilic compounds in the original sample to be 1:3. For the first time, KTA is applied to an aerosol with this level of complexity and displays its potential for providing physically-based constraints for GCM parameterizations of the aerosol indirect effect.

Citation: Asa-Awuku, A., Nenes, A., Sullivan, A. P., Hennigan, C. J., and Weber, R. J.: Investigation of molar volume and surfactant characteristics of water-soluble organic compounds in biomass burning aerosol, Atmos. Chem. Phys. Discuss., 7, 3589-3627, doi:10.5194/acpd-7-3589-2007, 2007.
 
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