![]() Moreover, studies on driven factors to changes in NO 2 can further detect the impacts of human and society activities on air quality. Several researches have analyzed the impact of the COVID-19 on environment or economy ( Liu et al., 2020 He et al., 2020) using NO 2 tropospheric vertical column density (TVCD) provided by earth-observing satellites such as the Ozone Monitoring Instrument (OMI) ( Levelt et al., 2018) or the Tropospheric Monitoring Instrument (TROPOMI) ( Veefkind et al., 2012) in early 2020, and found that the anti-pandemic measures could unintentionally bring about environmental benefits, such as the reduction of NO 2 or other air pollutants level ( Wang et al., 2020b Huang et al., 2020). Nitrogen dioxide (NO 2) is often used to characterize the fossil fuel usage level, which is related to economic activity. ![]() ![]() While some sectors are still feeling the pinch of the COVID-19 outbreak, more have emerged from the negative impacts faster and stronger than expected (NBSC, 2020). China's economy got off to a wobbly start in 2020 ( SCPRC, 2021).Īs the COVID-19 was gradually brought under control in second half of 2020, the limitation on human activities weakened and China's economy experienced a strong rebound in the fourth quarter. In turn, the demand for fossil fuels significantly reduced and the nitrogen oxides (NO + NO 2= NOx) emissions in China declined by 11.5% compared to the same period in 2019 ( Zheng et al., 2020). Under the combination effects of lockdown policy and Lunar New Year (LNY) holidays, human activities, especially industry and transportation, were greatly limited in early 2020 ( Lv et al., 2020). On 23 January 2020, the central government of China imposed a lockdown in Wuhan to fight against COVID-19, and other Chinese cities subsequently implemented similar measures ( Wikipedia, 2021). In December 2019, the coronavirus disease 2019 (COVID-19) was reported in Wuhan, China, and then became a global pandemic ( WHO, 2020 Wang et al., 2020a). More efforts are still required to stimulate low-pollution development. This revenge bounce of NO 2 indicates the emission reduction of NOx in lockdown period is basically offset by the recovery of economy, revealing the fact that China's economic development and NOx emissions are still not decoupled. On the basis of quantitative analysis, we find the rebound of NO 2 TVCD is mainly caused by the rapid recovery of economy especially in the fourth quarter, when contribution of industry and power plant on NO 2 TVCD continues to rise. By the end of 2020, the annual average NO 2 TVCD declines by only 3.4% in China mainland, much less than the reduction of 24.1% in the lockdown period. The NO 2 TVCD reveals a sharp drop, followed by small fluctuations and then a strong rebound when compared to 2019. Here we use satellite observations from Tropospheric Monitoring Instrument to study the year-round variation of the nitrogen dioxide (NO 2) tropospheric vertical column density (TVCD) in 2020. The lockdown policy deals a severe blow to the economy and greatly reduces the nitrogen oxides (NOx) emission in China when the coronavirus 2019 spreads widely in early 2020. ![]()
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