Abstract:

By utilizing the ground meteorological observation data from 12 national meteorological stations in Xianyang city from 1962 to 2021, alongside the ambient air quality monitoring data from 2015 to 2021, the daily atmospheric self-purification capacity from 1962 to 2021 was calculated. The mutation tests were employed using Mann-Kendall (M-K)and sliding t-test (MT) methods, and the spatial characteristics were studied. The results show that the air self-purification capacity in Xianyang city exhibits distinct annual, monthly, and seasonal patterns, with a decreasing trend observed in decadal variation. The climate tendency rate of the air self-purification capacity is -1.22×10⁴ km²·a^-1·(10 a)^-1. From 1962 to 2021, the overall trend has shown an initial increase, followed by a decrease, and then another increase, with the lowest year (2002) recording a 70% decrease compared to the highest year (1969). The sequence of atmospheric self-purification capacity from high to low is summer, spring, fall, winter. The correlation coefficient between the annual average wind speed and the annual average atmospheric self-purification capacity is 0.98. The correlation coefficient between the number of light wind days and the atmospheric self-purification capacity of the atmosphere is -0.91, with the self-purification capacity of non-light wind days being 6.2 times that of light wind days. The correlation coefficients between the number of precipitation days, daily precipitation, monthly precipitation, and atmospheric self-purification capacity were 0.23, 0.02, and 0.07, respectively. In terms of spatial distribution, the annual and seasonal average atmospheric self-purification capacity is generally higher in the east and lower in the west, as well as higher in the north and lower in the south. Regions such as Wugong, Xingping, Qindu, and Weicheng exhibit lower atmospheric self-purification capacity. Additionally, the Air Quality Index (AQI) and PM_2.5 concentration are inversely correlated with atmospheric self-purification capacity. The abrupt change year of annual atmospheric self-purification capacity was identified through two abrupt change tests in 2010, with spring and summer experiencing an abrupt change in 2011, and autumn and winter in 2010.

Key words: Atmospheric self-purification capacity, Meteorological elements, Ambient air quality, Mutations testing