The impact of anthropogenic emissions sectors on the weekly cycle of ambient NO2 across China

Nitrogen dioxide (NO 2 ) mainly originate from anthropogenic activities such as combustion of fossil fuels in road transport, industries, and thermal power plants. Since human activity in industrialized countries in general follows a seven-day cycle, NO 2 emissions are expected to be reduced during weekends (Saturday–Sunday), and thus display a weekly cycle with low levels on weekends and high on weekdays (Monday–Friday). However, as one of the regions suffering serious NO 2 pollution in the world, weekly cycle of China's NO 2 with significant weekend reduction has not been observed by using satellite measurements. In this study we used NO 2 column data from Tropospheric Monitoring Instrument (TROPOMI) and national and provincial statistics traffic and gross domestic product (GDP) data across China to investigate weekly cycle of NO 2 during the coronavirus disease 2019 (COVID-19) lockdown in the first quarter (Q1) of 2020, the subsequent economic recovery period in Q1 2021, and the impact period of the breakout of Omicron in Q1 2022. We find an increase in magnitude of weekend reduction in NO 2 levels by 8% over China in Q1 2020 compared to Q1 2019 due to the lockdown restrictions, and passenger traveled, freight traveled, and secondary industry contributed 9%, 66%, and 25% to this change, respectively. A decrease in weekend reduction by 7% in Q1 2021 was observed due to economic stimulus packages issued by governments. Changes in provincial-level weekly cycle of NO 2 were also calculated, as well as the three emission source sectors variations. • Traffic and GDP data have potential merit in estimating weekly cycle of NO 2 . • An increase in NO 2 weekend reduction by 8% over China during COVID-19 is found. • A decrease in NO 2 weekend reduction by 7% is found due to economic recovery. • Freight traffic has a greatest influence on unclear weekly cycle of NO 2 for China. • Impacts of traffic and industry in NO 2 weekly cycle depend on local emission sectors.