Characteristics of carbonaceous aerosols in Beijing based on two-year observation

Both organic carbon (OC) and elemental carbon (EC) play an important role in climate change and human health. In the present work, OC and EC analysis was done for size segregated aerosols collected in Beijing during a period of two years (2009-2011). Both OC and EC concentrations exhibited a bimodal size distribution with the fine mode at 0.43-0.65 mu m and the coarse mode at 4.7-5.8 mu m. The carbonaceous species were prone to enrich in the fine particles, with 22.5 +/- 11.5 and 15.9 +/- 5.6 mu g m(-3) of OC and 2.7 +/- 1.5 and 1.1 +/- 0.7 mu g m(-3) of EC in the fine particles (PM2.1) and the coarse particles (PM>2.1), respectively. OC and EC accounted for 39.9% and 8.2%, respectively, of PM mass in < 0.43 mu m size range. The highest concentrations of carbonaceous species were noticed during winter. An increase in carbonaceous species between the two-year observations may be mainly attributed to the increasing vehicular exhaust in Beijing and the increasing emissions from coal combustion in neighboring provinces. The concentrations of secondary organic carbon (SOC) were the highest in PM2.1 for winter and the lowest in PM>2.1 for autumn. SOC averagely contributed to OC (56.5%) in the aerosols of Beijing during the two-year observation.