In order to control the spread of the COVID-19 pandemic, the prevention and control measures of public health emergencies were initiated in all provinces of China in early 2020, which had a certain impact on air quality. In this study, taking Jiangsu Province in China as an example, the air pollution levels in different regions under different levels of pandemic prevention and control (PPC) measures are evaluated. The implementation of the prevention and control policies of COVID-19 pandemic directly affected the concentration of air pollutants. No matter what level of PPC measures was implemented, the air quality index (AQI) and pollutant concentrations of NO2, CO, PM10 and PM2.5 were all reduced by varied degrees. The higher the level of PPC measures, the greater the reduction was in air pollutant concentrations. Specifically, NO2 was the most sensitive to PPC policies. The concentrations of CO and atmospheric particulate matter (PM10 and PM2.5) decreased most obviously under the first and second level of PPC. The response speed of air quality to different levels of PPC measures varied greatly among different cities. Southern Jiangsu, which has a higher level of economic development and is dominated by secondary and tertiary industries, had a faster response speed and a stronger responsiveness. The results of this study reflect the economic vitality of different cities in economically advanced regions (i.e., Jiangsu Province) in China. Furthermore, the results can provide references for the formulation of PPC policies and help the government make more scientific and reasonable strategies for air pollution prevention and control.

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Compared with individual extreme events, compound events have more severe impacts on humans and the natural environment. This study explores the change in severity of compound extreme high temperature and drought/rain events (CHTDE/CHTRE) and associated influencing factors. The CHTDE and CHTRE intensified in most areas of China in summer (June–July August) during 1961–2014. Under global warming, the increased water-holding capacity of the atmosphere and the decreased relative humidity led to an increase in the severity of CHTDE. The severity of CHTRE is increased because of enhanced transient water vapor convergence and convective motion. Anthropogenic climate change, especially greenhouse gas forcing, which contributes 90% to the linear change in the severity of CHTDE and CHTRE, is identified as the dominant factor affecting the severity of CHTDE in China. In addition, the historical natural forcing (hist-NAT) may be related to the interannual-to-decadal variability in the severity of CHTDE/CHTRE.

<p>Extreme events seriously affect human health and natural environment. In the present study, several indexes that can describe the severity of compound extreme high temperature and drought/rainy events (CHTDE/CHTRE) are constructed based on copulas. According to observations, CHTDE and CHTRE have intensified in most areas of China during 1961–2014. The significant increase trend in the severity of CHTDE and CHTRE is basically consistent with simulations under historical anthropogenic forcing. This result proves that changes in CHTDE can be largely attributed to anthropogenic climate change. The historical greenhouse gas forcing is identified to be the dominant factor that affects the severity of CHTDE in China, particularly in the Tibetan Plateau and Northwest China. Moreover, the contribution of anthropogenic forcing to the linear change of the CHTRE severity in China is more than 90%. In addition, the ozone and land use signals also can be detected on change of CHTDE and CHTRE.</p>

Extreme events seriously affect human health and natural environment. In the present study, several indexes that can describe the severity of compound extreme high temperature and drought/rainy events (CHTDE/CHTRE) are constructed based on copulas. According to observations, CHTDE and CHTRE have intensified in most areas of China during 1961–2014. The significant increase trend in the severity of CHTDE and CHTRE is basically consistent with simulations under historical anthropogenic forcing. This result proves that changes in CHTDE can be largely attributed to anthropogenic climate change. The historical greenhouse gas forcing is identified to be the dominant factor that affects the severity of CHTDE in China, particularly in the Tibetan Plateau and Northwest China. Moreover, the contribution of anthropogenic forcing to the linear change of the CHTRE severity in China is more than 90%. In addition, the ozone and land use signals also can be detected on change of CHTDE and CHTRE.