Atmos. Chem. Phys. Discuss., 7, 9053-9092, 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.
Secondary organic aerosol in the global aerosol – chemistry transport model Oslo CTM2
C. R. Hoyle, T. Berntsen, G. Myhre, and I. S. A. Isaksen
Department of Geosciences, University of Oslo, Norway

Abstract. The global chemical transport model Oslo CTM2 has been extended to include the formation, transport and deposition of secondary organic aerosol (SOA). Precursor hydrocarbons which are oxidised to form condensible species include both biogenic species such as terpenes and isoprene, as well as species emitted predominantly by anthropogenic activities (toluene, m-xylene, methylbenzene and other aromatics). A model simulation for 2004 gives an annual global SOA production of approximately 55 Tg. Of this total, 2.5 Tg is found to consist of the oxidation products of anthropogenically emitted hydrocarbons, and about 15 Tg is formed by the oxidation products of isoprene. The global production of SOA is increased to about 76 Tg yr−1 by allowing semi-volatile species to condense on ammonium sulphate aerosol. This brings modelled organic aerosol values closer to those observed, however observations in Europe remain significantly underestimated, raising the possibility of an unaccounted for SOA source. Allowing SOA to form on ammonium sulphate aerosol increases the contribution of anthropogenic SOA from about 4.5% to almost 9% of the total production. The importance of NO3 as an oxidant of SOA precursors is found to vary regionally, causing up to 50%–60% of the total amount of SOA near the surface in polluted regions and less than 25% in more remote areas. This study underscores the need for SOA to be represented in a more realistic way in global aerosol models in order to better reproduce observations of organic aerosol burdens in industrialised and biomass burning regions.

Citation: Hoyle, C. R., Berntsen, T., Myhre, G., and Isaksen, I. S. A.: Secondary organic aerosol in the global aerosol – chemistry transport model Oslo CTM2, Atmos. Chem. Phys. Discuss., 7, 9053-9092, doi:10.5194/acpd-7-9053-2007, 2007.
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