Atmos. Chem. Phys. Discuss., 8, 20839-20867, 2008
www.atmos-chem-phys-discuss.net/8/20839/2008/
doi:10.5194/acpd-8-20839-2008
© Author(s) 2008. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Towards closing the gap between hygroscopic growth and activation for secondary organic aerosol – Part 2: Theoretical approaches
M. D. Petters1, H. Wex2, C. M. Carrico1, E. Hallbauer2, A. Massling2,3, G. R. McMeeking1,4, L. Poulain2, Z. Wu2, S. M. Kreidenweis1, and F. Stratmann2
1Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA
2Institute for Tropospheric Research, Leipzig, Germany
3now at: National Environmental Research Institute, Aarhus University, Roskilde, Denmark
4now at: Centre for Atmospheric Science, University of Manchester, Manchester, UK

Abstract. We examine the hygroscopic properties of secondary organic aerosol particles generated through the reaction of alpha-pinene and ozone using a continuous flow reaction chamber. The water activity versus composition relationship is calculated from measurements of growth factors at relative humidities up to 99.6% and from measurements of cloud condensation nuclei activity. The observed relationships are complex, suggesting highly non-ideal behavior for aerosol water contents at relative humidities less than 98%. We present two models that may explain the observed water activity-composition relationship equally well. The first model assumes that the aerosol is a pseudo binary mixture of infinitely water soluble compounds and sparingly soluble compounds that gradually enter the solution as dilution increases. The second model is used to compute the Gibbs free energy of the aerosol-water mixture and shows that the aerosol behaves similarly to what can be expected for single compounds that contain a certain fraction of oxygenated and non-polar functional groups.

Citation: Petters, M. D., Wex, H., Carrico, C. M., Hallbauer, E., Massling, A., McMeeking, G. R., Poulain, L., Wu, Z., Kreidenweis, S. M., and Stratmann, F.: Towards closing the gap between hygroscopic growth and activation for secondary organic aerosol – Part 2: Theoretical approaches, Atmos. Chem. Phys. Discuss., 8, 20839-20867, doi:10.5194/acpd-8-20839-2008, 2008.
 
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