NOxEmission Changes Over China During the COVID‐19 Epidemic Inferred From Surface NO2Observations

The COVID‐19 epidemic has substantially limited human activities and affected anthropogenic emissions. In this work, daily NOxemissions are inferred using a regional data assimilation system and hourly surface NO2measurement over China. The results show that because of the coronavirus outbreak, NOxemissions across the whole mainland China dropped sharply after 31 January, began to rise slightly in certain areas after 10 February, and gradually recover across the country after 20 February. Compared with the emissions before the outbreak, NOxemissions fell by more than 60% and ~30% in many large cities and most small to medium cities, respectively. Overall, NOxemissions were reduced by 36% over China, which were mainly contributed by transportation. Evaluations show that the inverted changes over eastern China are credible, whereas those in western China might be underestimated. These findings are of great significance for exploring the reduction potential of NOxemissions in China. In this study, we quantitatively estimate the impact of the COVID‐19 lockdown on NOxemissions over China based on nationwide surface hourly NO2monitoring data. We find that NOxemissions dropped sharply after 31 January and began to gradually recover after 20 February across the country; NOxemissions fell by more than 60% in many large cities and decreased by ~30% in most small to medium cities. Across the whole mainland China, NOxemissions were reduced by 36% due to the COVID‐19 lockdown. The spatiotemporal variations of NOxemissions across mainland China during COVID‐19 well inferred from surface NO2observationsNOxemissions fell by more than 60% in many large cities and by 36% across the whole mainland China due to the lockdownNOxemissions dropped sharply after 31 January and began to gradually recover after 20 February across the country