Continuous observation of black carbon aerosol during winter in urban Beijing, China

Abstract

Black carbon (BC) has a significant impact on air quality and atmospheric light absorption due to its unique physical properties. In this study, a ten-wavelength black carbon monitor was used to measure BC concentrations continuously during winter in urban Beijing. A comparison of BC concentrations was carried out between the ten-wavelength black carbon monitor and a multi-angle absorption photometer (MAAP) and a thermal optical transmission method carbon analyzer. The results showed significant correlations between BC measured by the MAAP, the thermal optical transmission method carbon analyzer and BC measured at the 660 nm wavelength using the ten-wavelength black carbon monitor. Obvious differences in BC concentrations were recorded at the different wavelength ranges. The BC concentrations observed in the visible ranges, near-infrared ranges and near-ultraviolet ranges were on average 3.1, 2.6, and 4.6 μg m−3, respectively. The differences between the absorption coefficient of BC370 nm and BC880 nm increased with the enhancement of OC:TC (ratio of organic carbon to total carbon) and PM2.5, indicating that organic matter had strong light absorption at near-ultraviolet wavelength. BC concentrations had clear diurnal variations with maxima at 0300 and minima at 1400 (Local time). In addition, potential contribution source areas of BC were also analyzed. This is the first time that BC measurements have been conducted using the ten-wavelength BC monitor, which provided more information of BC at different wavelengths compared to other methods.

Keywords

• Black carbon
• organic carbon
• Beijing
• absorption coefficient