Abstract:

Based on the National Air Quality Index (AQI), PM_2.5 mass concentration data, Global Data Assimilation System (GDAS) meteorological data from 2014 to 2018, and the backward trajectory model, the characteristics of PM_2.5 concentration changes in Huzhou city were analyzed. Eight heavy pollution processes that occurred in 5 years were screened out for transportation characteristics and potential source analysis. The results show that the frequency distribution of the daily average concentration of PM_2.5 in Huzhou city changes exponentially, and the high-frequency area corresponds mainly concentrations between 20-40 μg·m^-3. The pollutant mainly occurs in winter, with low concentration values in summer and early autumn. The diurnal variation of the hourly average concentration presents a bimodal distribution, in which the main peak appears at 10 o'clock, the auxiliary peak appears at 2 o'clock, and the valley is at 18 o'clock. The concentration is related to the change of NO₂ and SO₂. PM_2.5 in Huzhou city is mainly transported along the northwest and east path over a medium and long-distance. Among them, the northwest path transportation has a greater impact on the Huzhou area. The air mass in the eastward path passes over the sea surface, and it is fully mixed with the water vapor, which will aggravate the second generation and aging process of the particulate matter. The southwest-by-west and southerly paths also contribute to Huzhou's air pollution, but uncertainty remains, the southerly path appears as a clean passage in individual cases. The urban agglomeration along the northwest route is the main potential source area, and the high-value area is mainly concentrated in the central and western parts of Anhui province.

Key words: Heavily polluted weather, PM_2.5, Huzhou, Backward trajectory clustering