Assessment of air quality before and during the COVID-19 and its potential health impacts in an arid oasis city: Urumqi, China

As a key node city of the “Silk Road Economic Belt” Urumqi has been listed as one of the ten most polluted cities in the world, posing a serious threat to the urban environment and residents' health. This study analyzed the air quality before and during the COVID-19 (Coronavirus disease 2019) pandemic and its potential health effects based on the data of PM 2.5 , PM 10 , SO 2 , NO 2 , CO, and O 3 _8h levels from 10 air quality monitoring stations in Urumqi from January 1, 2017, to December 31, 2021. As per the results, the concentrations of the air pollutants PM 2.5 , PM 10 , SO 2 , NO 2 , CO, and O 3 _8h in Urumqi from 2017 to 2021 showed a cyclical trend, and the implementation of COVID-19 prevention and control measures could effectively reduce the concentration(ρ) of air pollutants. The mean value of ρ(PM 2.5 ) decreased from 2017 to 2021, whereas ρ(O 3 _8h) showed a waveform change trend (increased in 2017–2018, decreased in 2018–2020, and increased after 2020). Meanwhile, the maximum annual average values of ρ(PM 2.5 ) and ρ(O 3 _8h) for the six monitoring stations during 2017–2021 occurred at sites S2 (74.37 µg m −3 ) and S6 (91.80 µg m −3 ), respectively; rapid industrialization had a greater impact on PM 2.5 and O 3 _8h concentrations compared to commercial and residential areas. In addition, the air quality index data series can characterize the fluctuation trend of PM 2.5 . The high pollution levels (Class IV and V) of the air pollutants PM 2.5 and O 3 _8h in Urumqi have been decreasing annually, and good days can account for 80–95% of the total number of days in the year, indicating that the number of days with a potential threat to residents' health is gradually decreasing. Therefore, more attention should be paid in controlling and managing air pollution in Urumqi.