THE SPATIOTEMPORAL VARIATION OF HEAVY NO₂ POLLUTION CENTER (HPC): A CASE STUDY IN THREE CHINESE URBAN AGGLOMERATIONS

Abstract. Air pollution episode, which are periods with excessive air pollutants, can cause a sharp increase in mortality and morbidity. Nitrogen oxides have an adverse impact on human health and the environment. Previous studies mainly focus on the time period, the frequency, and the duration of heavy NO₂ pollution, while ignored its spatial extent which is pivotal in providing early warning and prediction. In this study, we investigated the spatiotemporal variation of the heavy NO₂ pollution extent (i.e., heavy pollution center), analyzed its association with meteorological condition and further predicted its distribution in the future. A case study in Jing-Jin-Ji (JJJ), Yangtze River Delta (YRD) and Pearl River Delta (PRD) urban agglomerations showed that the HPC exhibited evident seasonal (winter > summer) and inter-city (mega and medium cities > small cities) differences. In concretion analysis, the HPC areas were negatively correlated with temperature and precipitation, suggesting that dry and cold meteorological conditions were responsible for the severe NO₂ pollution events. Trend analysis showed that the small and medium cities may serve as the HPC in the future. During the 2005–2016, the medium and small cities in JJJ experience a more rapid increase in NO₂ concentration in comparison to mega cities. Meanwhile, in YRD and PRD, a more rapid decrease was witnessed in the mega cities. The results of this study would provide support for early warning and prediction of heavy air pollutants and offer scientific insights for air pollution episode management.