Untangle contributions of meteorology condition and human mobility to tropospheric NO(2) in Chinese mainland during COVID-19 pandemic in early 2020

Yuxiang, Zhang; Haixu, Bo; Zhe, Jiang; Yu, Wang; Yunfei, Fu; Bingwei, Cao; Xuewen, Wang; Jiaqi, Chen; Rui, Li

In early 2020, unprecedented lockdowns and travel bans were implemented in Chinese mainland to stop the spread of novel coronavirus (COVID-19), which have led to large reduction of anthropogenic emissions. This provided a unique opportunity to isolate the effects from emission and meteorology on tropospheric nitrogen dioxide (NO(2)). Comparing the atmospheric NO(2) in 2020 to 2017, we found the changes of emission have led to a -49.3 ± 23.5% reduction, which was ∼12% more than satellite observed reduction of -37.8 ± 16.3%. The discrepancy was mainly due to the changes of meteorology which have contributed to an 8.1 ± 14.2% increase of NO(2). We also revealed that the emission induced reduction of NO(2) 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(2) in 29 megacities which each has a population of over 8 million in Chinese mainland.