Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 2 2005 10.5194/acpd-5-1255-2005 http://www.atmos-chem-phys-discuss.net/5/1255/2005/ http://www.atmos-chem-phys-discuss.net/5/1255/2005/acpd-5-1255-2005.html http://www.atmos-chem-phys-discuss.net/5/1255/2005/acpd-5-1255-2005.pdf 1255 1283 2005-03-09 Naturally driven variability in the global secondary organic aerosol over a decade K. Tsigaridis J. Lathière M. Kanakidou D. A. Hauglustaine Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, POBox 1470, 71409 Heraklion, Greece LSCE, CNRS/CEA, l’Orme-des-Merisiers, 91191 Gif-sur-Yvette, France In order to investigate the variability of the secondary organic aerosol (SOA) distributions and budget and provide a measure for the robustness of the conclusions on human induced changes of SOA, a global 3-dimensional chemistry transport model describing both the gas and the particulate phase chemistry of the troposphere has been applied. The response of the global budget of SOA to temperature and moisture changes as well as to biogenic emission changes over a decade (1984–1993) has been evaluated. The considered emissions of biogenic non-methane volatile organic compounds (VOC) are driven by temperature, light and vegetation. They vary between 756 and 810 TgC y^-1 and are therefore about 5.5 times higher than the anthropogenic VOC emissions. All secondary aerosols (sulphuric, nitrates and organics) are computed on-line together with the aerosol associated water. Over the studied decade, the computed natural variations (8%) in the chemical SOA production from biogenic VOC oxidation equal the chemical SOA production from anthropogenic VOC oxidation. This computed variability results from a 7% increase in biogenic VOC emissions combined with 8.5% and 6% increases in the wet and dry deposition of SOA and leads to about 11.5% increase in the SOA burden of biogenic origin. The present study also demonstrates the importance of the hydrological cycle in determining the built up and fate of SOA in the atmosphere. It also reveals the existence of significant positive and negative feedback mechanisms in the atmosphere responsible for the non linear relationship between emissions of biogenic VOC and SOA burden.