Articles | Volume 11, issue 12
Atmos. Chem. Phys., 11, 5761–5782, 2011

Special issue: European Integrated Project on Aerosol-Cloud-Climate and Air...

Atmos. Chem. Phys., 11, 5761–5782, 2011

Research article 22 Jun 2011

Research article | 22 Jun 2011

In-cloud oxalate formation in the global troposphere: a 3-D modeling study

S. Myriokefalitakis2,1, K. Tsigaridis4,3, N. Mihalopoulos1, J. Sciare5, A. Nenes7,6,2, K. Kawamura8, A. Segers9, and M. Kanakidou1 S. Myriokefalitakis et al.
  • 1Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, 71003, P.O. Box 2208, Heraklion, Greece
  • 2Institute of Chemical Engineering and High Temperature Chemical Processes (ICE-HT), Foundation for Research and Technology Hellas (FORTH), Patras, 26504, Greece
  • 3Center for Climate Systems Research, Columbia University, New York, NY 10025, USA
  • 4NASA Goddard Institute for Space Studies, New York, NY 10025, USA
  • 5Laboratoire des Sciences du Climat et de l'Environnement (LSCE), CNRS/CEA, 91190 Gif sur Yvette, France
  • 6School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0100, USA
  • 7School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0100, USA
  • 8Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan
  • 9TNO Built Environment and Geosciences, Department of Air Quality and Climate, P.O. Box 80015, 3508 TA Utrecht, The Netherlands

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 = 1.16 ± 0.14, r2 = 0.36, N = 114) 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-cloud and less than 5 % is produced in aerosol water. About 62 % of the oxalate is removed via wet deposition, 30 % by in-cloud reaction with hydroxyl radical, 4 % by in-cloud reaction with nitrate radical and 4 % by dry deposition. The in-cloud global oxalate net chemical production is calculated to be about 21–37 Tg yr−1 with almost 79 % 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 0.2–0.3 Tg, i.e. 0.05–0.1 Tg-C that is about 5–9 % of model-calculated water soluble organic carbon burden.

Final-revised paper