Untangling the contributions of meteorological conditions and human mobility to tropospheric NO2 in Chinese mainland during the COVID-19 pandemic in early 2020

In early 2020, unprecedented lockdowns and travel bans were implemented in Chinese mainland to fight COVID-19, which led to a large reduction in anthropogenic emissions. This provided a unique opportunity to isolate the effects from emission and meteorology on tropospheric nitrogen dioxide (NO2). Comparing the atmospheric NO2 in 2020 with that in 2017, we found the changes of emission have led to a 49.3 +/- 23.5% reduction, which was similar to 12% more than satellite-observed reduction of 37.8 +/- 16.3%. The discrepancy was mainly a result of changes of meteorology, which have contributed to an 8.1 +/- 14.2% increase of NO2. We also revealed that the emission-induced reduction of NO2 has significantly negative correlations to human mobility, particularly that inside the city. The intra-city migration index derived from Baidu Location-Based-Service can explain 40.4% +/- 17.7% variance of the emission-induced reduction of NO, in 29 megacities, each of which has a population of over 8 million in Chinese mainland.

Automated summary

The reduction in emissions due to COVID-19 lockdowns in early 2020 in Chinese mainland led to a decrease in NO2, while changes in meteorology caused an increase in NO2 levels. Human activity, especially intra-city migration, was found to have a significant impact on the emission-induced reduction of NO2 in major cities in Chinese mainland.