We have made large-scale intensive observations, named the Integrated Measurement Program for Aerosol and Oxidant Chemistry in Tokyo (IMPACT) , at the University of Tokyo, RCAST in Tokyo in 2003 ∼ 2004 to understand key processes which control the abundances of different types of aerosols in urban air. Various kinds of aerosols in fine mode and their precursor gases were measured with high accuracies using the most advanced measurement techniques, including an aerosol mass spectrometer (AMS) . This paper is a summary of the important findings on carbonaceous aerosols (organic aerosols and elemental carbon) . First, we present systematic evaluations of the uncertainties in aerosol measurement. We then discuss the temporal variations and chemical composition of organic aerosols based on the observational data. Water solubility of secondary organic aerosol (SOA) is quantified. Recent results on modeling the distributions of SOA are presented. Finally, the diurnal and seasonal variations of elemental carbon (EC) are analyzed in terms of temporal variations of the EC emissions.
