Spatial and temporal variation characteristics of atmospheric NO 2 and SO 2 in the Beijing-Tianjin-Hebei region before and after the COVID-19 outbreak

Emergency response mechanisms were activated throughout China during the COVID-19 outbreak. It is different from the temporary, partial, and limited pollution control measures taken to ensure the regional environmental quality during several important events such as the 2008 Beijing Olympic Games and the 2014 Asia-Pacific Economic Cooperation (APEC). During the COVID-19 epidemic period, extensive movement of people and almost all unnecessary industrial production (necessary industrial production refers to the production of food, epidemic prevention materials, etc.) have been severely restricted, so transportation and industrial production have been greatly reduced. This is a rare extreme emission reduction scenario that presents a unique opportunity for atmospheric research. In this study, based on hourly mass concentration data of NO 2 and SO 2 from atmospheric monitoring sites in the Beijing-Tianjin-Hebei (BTH) region during the COVID-19 epidemic period, the changes in transportation and industrial production in the region, data statistics, and spatial analysis were used to analyze the pollution changes and their causes. The results indicate that the NO 2 and SO 2 concentrations in the BTH region decreased significantly during the epidemic period. The spatial distribution pattern of NO 2 pollution in the BTH region was “high in the southeast and low in the northwest,” and SO 2 pollution in the BTH region was high in the southern and eastern parts of Hebei. The initiation of emergency response level 1 had an obvious effect on reducing NO 2 and SO 2 pollution in the region, while the impact of emergency response level 2 and below was limited. Compared with the single traffic control, the comprehensive control, similar to the emergency response, had a better effect on reducing NO 2 pollution in the region. The control of major large cities in the region also had a certain effect on alleviating NO 2 and SO 2 pollution in the entire region. Moreover, for activities under short-term control, it is particularly important to guard against the “retaliatory growth” after the control is lifted. By reducing and controlling some polluting industries in industrial production, the degree of NO 2 and SO 2 pollution in the region can be effectively reduced. The manufacturing industry of chemical raw materials and the chemical products and non-metallic mineral products industry made a great contribution to the change in industrial source pollution emissions in the BTH region during the COVID-19 epidemic. Road traffic emissions remained an important source of NO 2 emissions in the BTH region during this period. NO 2 emission reduction can be effectively achieved by controlling road traffic and transportation.