Distinct Responses Of Urban and Rural O 3  Pollution With Secondary Particle Changes To Anthropogenic Emission Reductions: Insights From A Case Study Over North China

Abstract

Ozone (O3) pollution with increasing near-surface O3 levels has been an important environmental issue in China, although the anthropogenic emission reductions (AER) have improved air quality since 2013. This study analyzed the sensitivities of the atmospheric chemical environment focusing on the differentiated responses of urban and rural O3 pollution to the AER in North China, by conducting the simulation experiments with WRF-Chem under the scenario of AER with anthropogenic emission inventories of years 2012 and 2019. The results show that the unbalanced AER aroused more serious O3 pollution in urban and rural areas. The intense NO reduction was responsible for the significant increments of urban O3, while the falling NO2 and NO synergistically devoted to the slight O3 variations in rural areas. The AER induced the shift of the O3 formation from VOCs-limited to transition regimes in urban areas and the NOx-limited regime dominating rural areas over North China. Also, the AER reinforced the atmospheric oxidation capacity with the elevations of atmospheric oxidants O3 and ROx radicals, strengthening the chemical conversions to secondary inorganic particles. In both urban and rural areas, the sharp drop in SO2 caused a decrease in sulfate fraction, while the enhanced AOC accelerated the transformation to nitrate even when NOx was reduced. The AER induced nitrate to occupy the principal position in PM2.5 in urban and rural areas. The AER promoted and suppressed daytime and nighttime nitrate production in urban areas. Although the rural AOC increments were much lower comparatively, more vigorous conversion of secondary aerosols were found in the rural areas. This study reveals the distinct effects of AER in urban and rural atmospheric environment changes, with implications for an effective abatement strategy on O3 pollution.

Keywords: Emission reductions, O3 pollution episode, O3 formation sensitivity, Atmospheric oxidation capacity, Secondary aerosols