PM2.5 and O3 pollution during 2015–2019 over 367 Chinese cities: Spatiotemporal variations, meteorological and topographical impacts
2020
Zhao, Suping | Yin, Daiying | Yu, Ye | Kang, Shichang | Qin, Dahe | Dong, Longxiang
The strict Clean Air Action Plan has been in place by central and local government in China since 2013 to alleviate haze pollution. In response to implementation of the Plan, daytime PM₂.₅ (particulate matter with aerodynamic diameter less than 2.5 μm) showed significant downward trends from 2015 to 2019, with the largest reduction during spring and winter in the North China Plain. Unlike PM₂.₅, O₃ (ozone) showed a general increasing trend, reaching 29.7 μg m⁻³ on summer afternoons. Increased O₃ and reduced PM₂.₅ simultaneously occurred in more than half of Chinese cities, increasing to approximately three-fourths in summer. Declining trends in both PM₂.₅ and O₃ occurred in only a few cities, varying from 19.1% of cities in summer to 33.7% in fall. Meteorological variables helped to decrease PM₂.₅ and O₃ in some cities and increase PM₂.₅ and O₃ in others, which is closely related to terrain. High wind speed and 24 h changing pressure favored PM₂.₅ dispersion and dilution, especially in winter in southern China. However, O₃ was mainly affected by 24 h maximum temperature over most cities. Soil temperature was found to be a key factor modulating air pollution. Its impact on PM₂.₅ concentrations depended largely on soil depth and seasons; spring and fall soil temperature at 80 cm below the surface had largely negative impacts. Compared with PM₂.₅, O₃ was more significantly affected by soil temperature, with the largest impact at 20 cm below the surface and with less seasonal variation.
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