Size distribution and source of black carbon aerosol in
urban Beijing during winter haze episodes
Yunfei Wu1, Xiaojia Wang1, Jun Tao2, Rujin Huang3, Ping Tian4, Junji Cao3, Leiming Zhang5, Kin-Fai Ho6, and Renjian Zhang11Key Laboratory of Regional Climate-Environment for Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China 2South China Institute of Environmental Sciences, Ministry of Environmental Protection, Guangzhou, China 3Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, China 4Beijing Weather Modification Office, Beijing, China 5Air Quality Research Division, Science Technology Branch, Environment Canada, Toronto, Canada 6The Jockey Club School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China
Received: 05 Dec 2016 – Accepted for review: 05 Dec 2016 – Discussion started: 06 Dec 2016
Abstract. Black carbon (BC) plays an important role in the climate and environment due to its light absorption, which is greatly dependent on its physicochemical properties including morphology, size and mixing state. The size distribution of the refractory BC (rBC) in urban Beijing during the late winter in 2014 was revealed by measurements obtained using a single particle soot photometer (SP2), when the hazes occurred frequently. By assuming void-free rBC with a density of 1.8 g cm−3, the mass of the rBC showed an approximately lognormal distribution as a function of the volume-equivalent diameter (VED), for which there was a peak diameter of 213 nm. This size distribution agreed well with those observed in other urban areas of China. Larger VED values of the rBC were observed during polluted periods than on clean days, implying an alteration in the rBC sources, as the mass-size of the rBC from a certain source varied little once it was emitted into the atmosphere. The potential source contribution functions showed that air masses from the south to east of the observation site brought a higher rBC loading with more thick coatings and larger core sizes. The mean VED of the rBC (VEDrBC) presented a significant linear correlation with the number fraction of thickly coated rBC (NFcoated); the VED of the entirely externally mixed rBC was inferred as the y-intercept of the linear regression. This VED, with a value of ~150 nm, was considered as the typical mean VED of the rBC from local traffic sources in this study. Accordingly, the contribution of the local traffic to the rBC was estimated based on reasonable assumptions. Local traffic contributed 35 to 100 % of the hourly rBC mass concentration with a mean of 59 %, during this campaign. A lower local traffic contribution was observed during polluted periods, suggesting increasing contributions of other sources (e.g., coal combustion/biomass burning) to the rBC. The heavy pollution in Beijing was greatly influenced by other sources in addition to the local traffic.
Wu, Y., Wang, X., Tao, J., Huang, R., Tian, P., Cao, J., Zhang, L., Ho, K.-F., and Zhang, R.: Size distribution and source of black carbon aerosol in
urban Beijing during winter haze episodes, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1096, in review, 2016.