Atmos. Chem. Phys. Discuss., 11, 485-530, 2011
© Author(s) 2011. This work is distributed
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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.
In-cloud oxalate formation in the global troposphere: a 3-D modeling study
S. Myriokefalitakis1, K. Tsigaridis2,3, N. Mihalopoulos1, J. Sciare4, A. Nenes5,6, A. Segers7,8, and M. Kanakidou1
1Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, 71003, P.O. Box 2208, Heraklion, Greece
2Center for Climate Systems Research, Columbia University, New York, NY 10025, USA
3NASA Goddard Institute for Space Studies, New York, NY 10025, USA
4Laboratoire des Sciences du Climat et de l'Environnement (LSCE), CNRS/CEA, 91190 Gif sur Yvette, France
5School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0100, USA
6School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0100, USA
7TNO Built Environment and Geosciences, Department of Air Quality and Climate, P.O. Box 80015, 3508 TA Utrecht, The Netherlands
8Institute for Environment and Sustainability, European Commission, Joint Research Centre, 21027, Ispra, Italy

Abstract. Organic acids attract increasing attention as contributors to atmospheric acidity, secondary organic aerosol mass and aerosol hygroscopicity. Oxalic acid is globally the most abundant dicarboxylic acid, formed via chemical oxidation of gas-phase precursors in the aqueous phase of aerosols and droplets. Its lifecycle and atmospheric global distribution remain highly uncertain and are the focus of this study. The first global spatial and temporal distribution of oxalate, simulated using a state-of-the-art aqueous phase chemical scheme embedded within the global 3-dimensional chemistry/transport model TM4-ECPL, is here presented. The model accounts for comprehensive gas-phase chemistry and its coupling with major aerosol constituents (including secondary organic aerosol). Model results are consistent with ambient observations of oxalate at rural and remote locations (slope = 0.83 ± 0.06, r2 = 0.67, N = 106) and suggest that aqueous phase chemistry contributes significantly to the global atmospheric burden of secondary organic aerosol. In TM4-ECPL most oxalate is formed in-clouds and less than 10% is produced in aerosol water. About 61% of the oxalate is removed via wet deposition, 35% by in-cloud reaction with hydroxyl radical and 4% by dry deposition. The global oxalate net chemical production is calculated to be about 17–27 Tg yr−1 with almost 91% originating from biogenic hydrocarbons, mainly isoprene. This condensed phase net source of oxalate in conjunction with a global mean turnover time against deposition of about 5 days, maintain oxalate's global tropospheric burden of 0.24–0.39 Tg that is about 13–19% of calculated total organic aerosol burden.

Citation: Myriokefalitakis, S., Tsigaridis, K., Mihalopoulos, N., Sciare, J., Nenes, A., Segers, A., and Kanakidou, M.: In-cloud oxalate formation in the global troposphere: a 3-D modeling study, Atmos. Chem. Phys. Discuss., 11, 485-530, doi:10.5194/acpd-11-485-2011, 2011.
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