Simulating secondary organic aerosol in a 3-D Lagrangian chemistry transport model using the reduced Common Representative Intermediates mechanism (CRI v2-R5)

A secondary organic aerosol (SOA) code, coupled to the reduced Common Representative Intermediates chemical mechanism (CRI v2-R5), has been used in the global 3-D chemistry-transport model. STOCHEM, to simulate the global distribution of organic aerosol (OA) mass loadings. The SOA code represents the gas-to-aerosol partitioning of products formed over several generations of oxidation of a variety of organic precursors emitted from anthropogenic, biogenic and biomass burning sources. The model also includes emissions of primary organic aerosol (POA), based on the AeroCom inventory and the Global Fire Emissions database (GFED). The calculated burdens for POA, 0.89 Tg, and SOA, 0.23 Tg, are well within the range of values that have been reported in previous modelling studies. The calculated SOA annual in-situ production of 22.5 Tg yr(-1) also falls within the 8-110 Tg yr(-1) range calculated by other models, but is somewhat lower than observationally-constrained top-down estimates which have been reported recently. The oxidation of biogenic precursors is found to account for about 90% of the global SOA burden, and this makes a substantial contribution to the highest annual mean surface OA concentrations (up to 8 mu g m(-3)), which are simulated in tropical forested regions. Comparison of the simulated OA mass loadings with surface observations from a variety of locations indicate a good description of the OA distribution, but with an average underestimation of about a factor of 3. Sustained formation of SOA into the free troposphere is simulated, with important contributions from second and third-generation products of terpene oxidation in the upper troposphere. Comparison of the simulated OA mass loadings with vertical profiles from the ACE-Asia campaign indicates a very good description of the relative variation of OA with altitude, but with consistent underestimation of about a factor of 5. Although the absolute magnitude of the global source strength is underestimated, this consistency nonetheless provides support for an important role for multigenerational oxidation chemistry as a large source of SOA in the free troposphere, and lends credence to the necessity of representing condensable material formed over several generations of VOC oxidation in global chemistry-transport models. (C) 2011 Published by Elsevier Ltd.