Black carbon aerosol (BC) has emerged as a major contributor to global climate change, only second to CO₂ as the main driver of the global warming. BC is from the incomplete combustion of fossil fuels, biofuel, and biomass. By strongly absorbing solar radiation, BC can heat the atmosphere, affect its stability, further deteriorating air quality. The climatic and environmental effects of BC were determined by its loading in the atmosphere and scientists found its impacts could be also importantly affected by its microphysical characteristics such as particle size and mixing state.

Dr. WU Yunfei, with the Institute of Atmospheric Physics, Chinese Academy of Science, conducted long-term observations of BC loading and microphysical properties in urban Beijing, by using a single-particle soot photometer (SP2). In a recent study published in Environmental Pollution, he and his collaborators reported temporal variations of BC loading and microphysical properties.

"We observed evident decreases of BC loading in the atmosphere of urban Beijing since the implementation of China's Action Plan of Prevention and Control of Air Pollution in 2013." said Dr. WU. Apparently, strict emission controls contributed to the decrease. The team also found that emission control measures had impacts on BC size and mixing state. The BC aerosols became "slim", appearing with smaller core sizes and less coatings.

This phenomenon was more pronounced after the comprehensive implementation of the "coal to electricity" measures in Beijing and surrounding areas from 2016. "Coal combustion and biomass burning likely emitted more BC aerosols with larger core sizes and thicker coatings than vehicle exhaust." said Dr. WU.

A diagram of variations in BC aerosol core sizes and mixing states, and their relationship with emission source changes. (Image by WU Yunfei)

The team pointed out that the reduction of the thickly coated BC would further lead to a decline of solar radiation absorption by atmospheric aerosols beyond the decline resulting from the BC loading itself.

The research, published in Environmental Pollution, was funded by the National Key Research and Development Project (2019YFA0606801) and the National Natural Science Foundation of China (41775155, 41830966).

Citation: Wu YF*, Xia YJ, Zhou C, Tian P, Tao J, Huang R-J, et al., 2021: Effect of source variation on the size and mixing state of black carbon aerosol in urban Beijing from 2013 to 2019: Implication on light absorption. Environmental Pollution, 270, 116089, https://doi.org/10.1016/j.envpol.2020.116089.

Media contact: Ms. LIN Zheng, jennylin@mail.iap.ac.cn