To understand the concentrations and sources of carbonaceous aerosols in Northern China, real-time, semi-online, hourly measurements of PM2.5 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 PM2.5 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.
