Abstract:

Based on the China high air pollutants (CHAP) dataset from 2000 to 2023, this study identifies wintertime air pollution events in the urban agglomeration on the northern slope of Tianshan Mountains (Xinjiang, China) using the air quality index (AQI) and analyzes their spatiotemporal patterns (annual mean number of days, annual mean frequency, maximum duration, and intensity). The results demonstrated that (1) PM_2.5 was the dominant air pollutant in the urban agglomeration on the northern slope of Tianshan Mountains, present on more than 95% of the polluted days (AQI>100). (2) A climatological analysis revealed that pollution intensity peaks in the Urumqi-Changji-Shihezi region, where the long-term annual mean AQI exceeds 190 and the annual mean number of days accounts for more than 80% of the winter period. Mild pollution events (101≤AQI≤150) are especially frequent and widespread, with an annual mean of 25.7 days, a maximum annual mean frequency of 17.4 occurrences per year, and a maximum duration of up to 29.0 days. Moderate events (151≤AQI≤200) predominantly occur in the central and eastern subregions, averaging 5 days per year with a maximum annual mean frequency of 14.5 occurrences per year and a maximum duration of up to 12.3 days. In contrast, heavy and severe events (AQI≥201) are concentrated in the Urumqi-Changji-Shihezi region, where AQI peaks can exceed 500. The maximum duration of these events is 11.3 days, exhibiting a “short-duration, high-intensity” evolution pattern. (3) Mild and moderate pollution events have declined in 75.8% of the polluted regions in the urban agglomeration on the northern slope of Tianshan Mountains, but heavy and above pollution events have increased in the Urumqi-Changji-Shihezi core. (4) The characteristics of air pollution events among the nine key cities in the urban agglomeration on the northern slope of Tianshan Mountains varied significantly. Urumqi, Changji and Shihezi are most severely affected, followed by Wujiaqu, Kuytun, and Fukang, while Usu, Karamay, and Bole maintaine the cleanest air. The intensity, annual mean number of days, annual mean frequency, and maximum duration of moderate to severe pollution events in the Urumqi-Changji-Shihezi region are significantly higher than those in other cities, whereas Bole and Karamay are primarily affected by light pollution.

Key words: air pollution events, CHAP dataset, air quality index (AQI), spatiotemporal evolution characteristics, urban agglomeration on the northern slope of Tianshan Mountains