Characteristics and relevant remote sources of black carbon aerosol in Shanghai

Black carbon (BC) aerosol was measured continuously at an urban site in Shanghai (31°18′N, 121°30′E) from January 2011 to January 2012, and the characteristics and relevant remote sources of BC were examined. Daily BC concentrations varied within the range of 0.3–11.4μgm−3 with an annual average of 2.3μgm−3. Comparably, monthly BC concentrations were usually high in the dry season (November–April) but low in the wet season (May–October). Hourly BC showed a similar diurnal pattern with two peaks, one at 7:00–9:00 LT and another at 19:00–21:00 LT, in the four seasons. BC level was always relatively higher during daytime than nighttime. There also existed a workday/weekend difference of BC due to anthropogenic activities. The correlation analyses between BC and meteorological factors indicated that (1) wind speed was an important contributor to BC diffusion in the boundary atmosphere, (2) atmospheric visibility was not highly sensitive to BC, and (3) northwesterly, westerly and southwesterly wind directions related closely to BC. The increase of BC is likely associated with fossil fuel combustion during the winter heating period and agricultural waste burning over the surrounding areas during the summer harvest period, as well as the air masses originating from and/or transiting through these regions.