Abstract
Abstract. The Chinese government has made many efforts to mitigate fine particulate matter pollution in recent years by taking strict measures on air pollutant reduction, which has generated the nationwide improvements in air quality since 2013. However, under the stringent air pollution controls, how the wintertime PM2.5 concentration (i.e., the mass concentration of atmospheric particles with diameters less than 2.5 µm) varies and how much the meteorological conditions contribute to the interannual variations in PM2.5 concentrations are still unclear, and these very important for the local government to assess the emission reduction of the previous year and adjust mitigation strategies for the next year. The effects of atmospheric circulation on the interannual variation in wintertime PM2.5 concentrations over the Beijing–Tianjin–Hebei (BTH) region in the period of 2013–2018 are evaluated in this study. Generally, the transport of clean and dry air masses and an unstable boundary layer in combination with the effective near-surface horizontal divergence or pumping action at the top of the boundary layer benefits the horizontal or vertical diffusion of surface air pollutants. Instead, the co-occurrence of a stable boundary layer, frequent air stagnation, positive water vapor advection and deep near-surface horizontal convergence exacerbate the wintertime air pollution. Favorable circulation conditions lasting for 2–4 d are beneficial for the diffusion of air pollutants, and 3–7 d of unfavorable circulation events exacerbates the accumulation of air pollutants. The occurrence frequency of favorable circulation events is consistent with the interannual variation in seasonal mean PM2.5 concentrations. There is better diffusion ability in the winters of 2014 and 2017 than in other years. A 59.9 % observed decrease in PM2.5 concentrations in 2017 over the BTH region could be attributed to the improvement in atmospheric diffusion conditions. It is essential to exclude the contribution of meteorological conditions to the variation in interannual air pollutants when making a quantitative evaluation of emission reduction measurements.
Highlights
Rapid economic development and associated emissions have led to recent severe air pollution over China, which has become a central issue of concern for the public and governments (Mu and Zhang, 2014; Song et al, 2018; Tao et al, 2018; Wang et al, 2018b, 2015; Zhang et al, 2014; Zhao and Garrett, 2015)
It is essential to exclude the contribution of meteorological conditions to the variation in interannual air pollutants when making a quantitative evaluation of emission reduction measurements
The high emissions of primary fine particulate matters and its precursors are considered as internal factors of severe PM2.5 pollution in China; emission reduction is the most direct and effective way to improve local air quality
Summary
Rapid economic development and associated emissions have led to recent severe air pollution over China, which has become a central issue of concern for the public and governments (Mu and Zhang, 2014; Song et al, 2018; Tao et al, 2018; Wang et al, 2018b, 2015; Zhang et al, 2014; Zhao and Garrett, 2015). Zhao et al, 2018; Hong et al, 2019; Zhang et al, 2017; Hu et al, 2019). They are efficient in scattering and absorbing solar radiation and are involved in climate change by changing the surface energy budget To mitigate PM2.5 pollution, the Chinese government issued the Air Pollution Prevention and Control Action Plan (hereinafter referred to as the Clean Air Plan) in 2013, which required the Beijing–Tianjin–Hebei (BTH) region, Yangtze River Delta and Pearl River Delta to reduce their PM2.5 concentrations by 15 %–25 % from 2013
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