Modal Characteristics of Elemental and Organic Carbon in an Urban Location in Guangzhou, China

摘要

Carbonaceous matter is a major constituent in urban aerosols, especially in those collected in China. The size distributions of elemental carbon (EC) and organic carbon (OC) in the range of 0.01-18 μm were measured in an urban location in Guangzhou, China in July 2006. The EC size distribution in the accumulation-mode size was characterized by three significant modes with mass median aerodynamic diameters (MMAD) of ~0.15 μm, ~0.40 μm, and ~0.90 μm, with the second one being the most prominent and accounting for approximately half of the total EC mass. The coexistence of the first two accumulation modes in Guangzhou's urban atmosphere could be explained to be a result of emissions from vehicles operating at different loadings. The dominance of the EC accumulation mode at ~0.40 μm has not often been reported in studies conducted in developed countries, but this observation is consistent with EC size distributions measured in a roadway tunnel in this region. This information is important when modeling the role of EC in modulating the radiative balance and investigating the health effects of EC. The third accumulation mode was postulated to be a result of in-cloud processing after emission. OC had the same size modes as EC but different mass distributions among the modes. The carbonaceous materials in the nucleation mode were dominated by OC. Among particles in the accumulation size range, the OC/EC ratio was higher in the third accumulation mode (MMAD: 0.90 /on) than in the first two accumulation modes, suggesting that in-cloud processing was an important pathway for accumulating OC mass during atmospheric processing of EC particles.