ORISAM-TM4: a new global sectional multi-component aerosol model including SOA formation - Focus on carbonaceous BC and OC aerosols

Few global aerosol models deal with size differentiated inorganic/organic particles. Among them, still fewer ones explicitly treat secondary organic aerosol (SOA) formation. In this context, we have coupled the global chemistry-transport model (CTM) TM4 (Van Velthoven et al., 1996) and the aerosol sectional model ORISAM (ORganic and Inorganic Sectional Aerosol Model, Bessagnet et al., 2002). This new aerosol model ORISAM-TM4 can accommodate aerosol size distributions with a variable number of diameter sections (bins) between 0.04 mu m and over 10 mu m and detailed organic/inorganic chemistry coupled with optional gas schemes. Two model versions are presented: a tracer version and a fully detailed eight-bin version with SOA formation. Focus is made on carbonaceous BC (black carbon) and OC (organic carbon) aerosols. First, significant developments both in ORISAM and in TM4 are discussed in line with the incorporation of updated emission inventories of BC and primary OC (OCp). Then, general comparisons are made between simulated BC and OC concentrations in air and precipitation against worldwide measurements. Also for BC, sensitivity tests using different updated fossil fuel emission inventories are focused over Europe, where emission controls make great strides. The tracer version appears generally satisfactory for BC mostly at background and remote sites, but not for total OC. For this latter, quite significant improvements result from the incorporation of SOA formation in ORISAM-TM4, instead of estimating OC as being simply proportional to OCp, as done in most existing models. Conclusions and prospects are then given.