To understand the concentrations and sources of carbonaceous aerosols in Northern China, real-time, semi-online, hourly measurements of PM_2.5 compositions were conducted at an urban site in Wuqing, Tianjin from December 31, 2011 to January 11, 2012. The mean concentrations of EC and OC in Wuqing were 6.0±4.8 and 21.5±19.2 μg C/m³ respectively, which constituted 8% and 30% of the total measured PM_2.5 constituent mass. The mean concentration of WSOC was 14.3±11.8 μg C/m³, which constituted 67% of the mean OC concentration. During the observation period, the large variability of pollutant concentrations were mainly driven by synopticscale meteorological events. As a result, the diurnal patterns of EC, OC, and WSOC were relatively indistinct. The observed mass ratios of OC/EC was relatively stable throughout the observation period and averaged 3.9. Based on correlation analysis with other tracer constituents, it is found that the wintertime carbonaceous aerosols in Wuqing came mainly from biomass burning emissions and experienced significant aging. Roughly half of the OC were from biomass burning; the other half were from secondary formation processes.

The κ-K?hler theory and a simulation of the aerosol mass concentrations in China for the year 2006 were used to calculate the number concentration of cloud condensation nuclei (CCN) in China and evaluate the contribution of organic aerosol (OA). The number concentrations of CCN in China show a west-to-east gradient, due to the stronger anthropogenic emissions in eastern China. Assuming that all aerosol chemical components are externally mixed, the number concentrations of CCN are 0.9×10³-1.2×10³ cm^-3 seasonally, and OA contributes 30% to the annual mean. Assuming that OA components are internally mixed, while inorganic aerosols are externally mixed, the number concentrations of CCN are 0.9×10³-1.1×10³ cm^-3, and OA contributes 28% to the annual mean. Though the differernce of annual average contribution of OA to CCN number is small when OA is external and internal mixed, there is large different spatially in summer and winter due to more secondary OA in summer and more primary OA in winter. The results show that OA are important sources of CCN in China.