Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 1 2005 10.5194/acpd-5-755-2005 http://www.atmos-chem-phys-discuss.net/5/755/2005/ http://www.atmos-chem-phys-discuss.net/5/755/2005/acpd-5-755-2005.html http://www.atmos-chem-phys-discuss.net/5/755/2005/acpd-5-755-2005.pdf 755 794 2005-02-11 Assessment of the reduction methods used to develop chemical schemes: building of a new chemical scheme for VOC oxidation suited to three-dimensional multiscale HO_x-NO_x-VOC chemistry simulations S. Szopa B. Aumont S. Madronich Laboratoire Interuniversitaire des Systèmes Atmosphériques UMR CNRS 7583, Université Paris 7 et Paris 12, 94010 Créteil Cedex, France National Center for Atmospheric Research Atmospheric Chemistry Division, P.O. Box 3000, Boulder, Colorado 80307, USA now at: Laboratoire des Sciences du Climat et de l’Environnement UMR CNRS/CEA 1572, L’Orme des Merisiers &\ndash; bat. 701, 91191 Gif-sur-Yvette, France The objective of this work was to develop and assess an automatic procedure to write reduced chemical schemes for modeling gaseous photooxidant pollution at different scales. The method is based on (i) the development of a tool for writing the fully explicit schemes 5 for VOC oxidation and (ii) the assessment of reduced schemes using the fully explicit scheme as a reference. The reference scheme contained ca. seventy emitted VOCs chosen to be representative of both anthropogenic and biogenic emissions, and their atmospheric degradation chemistry involving more than two million reactions and 350 000 species was written using an expert system generator approach. 10 Three methods were applied to reduce the size of chemical schemes: (i) use of operators, based on the redundancy of the reaction sequences involved in the VOC oxidation, (ii) lumping of primary species having similar reactivities and (iii) lumping of secondary products into surrogate species. The number of species in the final reduced scheme is 150, i.e. low enough for 3-D modeling purposes using CTMs. Comparisons 15 between the fully explicit and reduced schemes, carried out with a box model for several typical tropospheric conditions, showed that the reduced chemical scheme accurately predicts ozone concentrations and some other aspects of oxidant chemistry for both polluted and clean tropospheric conditions.