Characterizing lead-rich particles in Beijing's atmosphere following coal-to-gas conversion: insights from single-particle aerosol mass spectrometry

Abstract. Coal-to-gas (CTG) policies are important energy transformation strategies for addressing air pollution issues, but how well they improve atmospheric lead (Pb) pollution remains poorly understood. By the end of 2018, Beijing had achieved coal-free status in urban and plain areas. The mixing state and atmospheric chemical processes of Pb-rich particles in Beijing were monitored using single-particle aerosol mass spectrometry (SPAMS) in 2019. Based on a large dataset of mass spectra, this study finds that the number fractions of Pb-rich particles, as well as two specific types of Pb-rich particles (K-Na-EC and K-OC, where EC and OC denote elemental and organic carbon, respectively) related to coal combustion during the official Beijing heating period, show lower number fractions than those after the heating period. Based on concentration-weighted trajectory plots, the results indicate that lead aerosols mainly derive from transmission from surrounding provinces. Lead nitrate is one of the important forms of lead in aerosol particles, particularly as a result of photo-chemical reactions in the spring, fall, and winter. Due to nitrate decomposition during high temperatures, the aqueous reaction mechanism contributes more to lead nitrate during the summer. These results improve our understanding of the seasonal distribution, formation mechanisms, and influencing factors of toxic Pb-containing particles after CTG.