Atmos. Chem. Phys. Discuss., 9, 2823-2853, 2009
www.atmos-chem-phys-discuss.net/9/2823/2009/
doi:10.5194/acpd-9-2823-2009
© Author(s) 2009. 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.
Hydration increases the lifetime of HSO5 and enhances its ability to act as a nucleation precursor – a computational study
T. Kurtén1, T. Berndt2, and F. Stratmann
1Department of Physics, P.O. Box 64, 00014 University of Helsinki, Helsinki, Finland
2Leibniz-Institut für Troposphärenforschung e.V., Permoserstr. 15, 04318 Leipzig, Germany

Abstract. Recent experimental findings indicate that HSO5 radicals are likely to play a key role in the nucleation of atmospheric SO2 oxidation products. HSO5 radicals are metastable intermediates formed in the SO2 oxidation process, and their stability and lifetime are, at present, highly uncertain. Previous high-level computational studies have predicted rather low stabilities for HSO5 with respect to dissociation into SO3+HO2, and have predicted the net reaction HSO3+OH → SO3+HO2 to be slightly exothermal. However, these studies have not accounted for hydration of HSO5 or its precursor HSO3. In this study, we have estimated the effect of hydration on the stability and lifetime of HSO5 using the advanced quantum chemical methods CCSD(T) and G3B3. We have computed formation energies and free energies for mono- and dihydrates of OH, HSO3, HSO5, SO3 and HO2, and also reanalyzed the individual steps of the HSO3+O2 → HSO5 → SO3+HO2 reaction at a higher level of theory than previously published. Our results indicate that hydration is likely to significantly prolong the lifetime of the HSO5 intermediate in atmospheric conditions, thus increasing the probability of reactions that form products with more than one sulfur atom. Kinetic modeling indicates that these results may help explain the experimental observations that a mixture of sulfur-containing products formed from SO2 oxidation by OH radicals nucleates much more effectively than sulfuric acid taken from a liquid reservoir.

Citation: Kurtén, T., Berndt, T., and Stratmann, F.: Hydration increases the lifetime of HSO5 and enhances its ability to act as a nucleation precursor – a computational study, Atmos. Chem. Phys. Discuss., 9, 2823-2853, doi:10.5194/acpd-9-2823-2009, 2009.
 
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