Identification of NO2 and SO2 over China: Characterization of polluted and hotspots Provinces

Increasing emissions of aerosol and trace gases (e.g. nitrogen dioxide: NO2 and sulfur dioxide: SO2) have resulted in severe air pollution in China due to its rapid industrialization, economic growth, and urbanization. This resulted in numerous environmental and health problems, and poor air quality mainly in industrial areas and major cities. This study identifies long-term (2005‒2020) Ozone Monitoring Instrument (OMI) based NO2 and SO2 pollution hotspots across China by analyzing spatiotemporal distributions and variations, with characterization of polluted provinces, SO2/NO2 ratio, trend, and assessing how effective China’s Air Pollution Control Policy (APCP) is on NO2 and SO2. Results show that NO2 and SO2 pollution hotspots were seen in China's central (Hubei), eastern (Anhui, Jiangsu, Shandong, Zhejiang), northern (Beijing, Hebei, Henan, Shanxi, Tianjin), northeast (Liaoning, Jilin), northwestern (Urumqi), southern (Guangdong, Hong Kong), and southwest (Chongqing, Sichuan). However, the pollution level was higher in winter, followed by autumn, spring, and summer. China’s eight provinces (Tianjin, Shanghai, Shandong, Jiangsu, Beijing, Hebei, Hong Kong, and Henan) were identified as extremely polluted with high NO2 levels ranging from 16.86 − 9.75 (1015 molecules/cm2), whereas Shandong, Tianjin, Hebei, Beijing, Henan, Shanxi, Jiangsu, Shanghai, Anhui, and Liaoning were deemed to extremely polluted provinces with high SO2 levels ranging from 20.62 − 14.30 (1015 molecules/cm2). Moreover, the SO2/NO2 ratio for 27 Chinese provinces fluctuates between 1.02 to 4.98, indicating industries emit more SO2 than NO2. Finally, China’s air pollution control policies (APCP) led to the largest annual reductions in NO2 during the 12th five-year plan (FYP) (6