Fig. 1. Location of the study area and distribution of the stations in Xi'an

Fig. 2. Comparison of AQI averages in Xi'an during the corresponding study periods in different years

Fig. 3. Comparison of AQI averages for the two outbreak control periods in 2020 (a) and 2022 (b) compared to the same time period in other years

Fig. 4. Comparison of the number of days with different air quality level in Xi'an during the strict pandemic control period of 2020 and 2022

Fig. 5. Comparison of pollutant concentration distribution in Xi'an at different stages from 2019 to 2022

Fig. 6. Comparison of main pollutant concentrations in Xi'an during different pandemic prevention stages from 2019 to 2022

Fig. 7. Radar plot of pollutant characteristics during strict epidemic control period in Xi'an in 2020 (a) and 2022 (b)

Fig. 8. Comparison of diurnal variations of AQI, precipitation and average temperature (a) with wind speed and relative humidity (b) during the study period

Fig. 9. Rose chart of wind direction during the study period during the research period in Xi'an

Fig. 10. Cluster analysis of backward trajectory at 500 m height during strict epidemic control period in Xi'an in February 2020 (a) and January 2022 (b)

Fig. 11. Topographic map of Xi'an City

Fig. 12. Comparison of inner city travel intensity during Spring Festival in Xi'an during the study period