Fig 1.
Map of study area ((a)Location and distribution of monitoring stations; (b)Orographic distribution in Urumqi and its surrounding areas).
Table 1.
Standard of air quality index [24,25] (GB3095-2012 environmental air quality standard).
Fig 2.
Inter-annual variations of major air pollutants in Urumqi.
Fig 3.
Monthly changes of major air pollutants in Urumqi.
Fig 4.
Histogram of daily SO2 concentration distribution in Urumqi.
Table 2.
The Statistical characteristics of variation of main pollutant concentrations in Urumqi.
Fig 5.
Daily changes of atmospheric pollutants in Urumqi.
Fig 6.
Daily changes of AQI in Urumqi.
Fig 7.
Frequency of pollution levels and cumulative percentage changes.
Table 3.
Correlation coefficients between main pollutants and meteorological factors in Urumqi.
Fig 8.
Variations of AQI and concentrations of PM2.5 and PM10 during the two air pollution events emerged from November 25th to December 2nd, 2018.
Fig 9.
Weather conditions in Urumqi and its surrounding areas from November 25th to December 2nd, 2018.
Fig 10.
Backward trajectory cluster distribution.
Table 4.
Distribution characteristics and average pollutant concentration of all backward trajectory.