## 1 Introduction
In other words, lower atmospheric self-purification capacity means a higher mass concentration of pollutants and vice versa ([PERSON] et al., 2019) [6]. So far, most scholars agree on the impact of atmospheric self-purification capacity on environmental pollution. To put it in another way, the improvement of atmospheric self-purification capacity plays a vital role in mitigating air pollution. Chinese scholars mostly take a city or region in China as a research object, analyze the change characteristic of atmospheric self-purification capacity, discuss the relationship between atmospheric self-purification capacity index and air quality in the sample regions, and draw similar conclusions. For example, scholars observe that in Tianjin when the atmospheric self-purification capacity remains low, the heavy-pollution events are most likely to occur ([PERSON] et al., 2019) [6]. In Hohhot, the atmospheric self-purification capacity index forms a negative correlation with air pollution index ([PERSON] et al., 2020) [7]. In the Yellow River Basin and main urban districts of Zhengzhou, the atmospheric self-purification capacity index forms a significant negative correlation with PM2.5 concentration, or when the atmospheric self-purification capacity index reaches a high level, the corresponding PM2.5 concentration remains low, with good air quality ([PERSON], 2021 [8]; [PERSON], 2022 [9]). [PERSON] et al. (2021) argue that a low atmospheric self-purification capacity index means weak air diffusion capacity that hinders the removal and diffusion of pollutants, with high air quality index. A high atmospheric self-purification capacity index promotes the ventilation and diffusion of pollutants and the removal capacity of precipitation [10]. Under what conditions can atmospheric self-purification capacity play a better role in controlling environmental pollution? As scholars conclude, the impact of atmospheric self-purification capacity on environmental pollution is restricted by multiple factors. The first ones are meteorological factors. Meteorological conditions, e.g., temperature inversion, low pressure, high humidity, weak wind, stable atmospheric stratification, low mixing-layer thickness, and weak precipitation, easily cause the accumulation of pollutants and constitute major meteorological factors for heavy pollution weather ([PERSON] et al., 2015) [11]. When the emission of external pollutants remains relatively stable, the degree and change of air pollution mostly hinge on meteorological factors, or the dilution effect of atmospheric self-purification capacity on pollutants varies with different meteorological conditions ([PERSON] et al., 2018) [12]. Season serves as an important factor that affects meteorology. For example, Linfen City, Shanxi Province, has the highest wind speed, the lowest relative humidity, the highest mixing-layer height, and the best atmospheric self-purification capacity in spring ([PERSON] et al., 2019) [13]. Heilongjiang Province has the highest atmospheric self-purification capacity in spring, higher in autumn, and the lowest in winter ([PERSON] et al., 2020) [14]. Xinjiang has a high atmospheric self-purification capacity in spring and summer, and a low atmospheric self-purification capacity in autumn and winter ([PERSON] et al., 2021) [15]. Spatial changes also affect atmospheric self-purification capacity. In China, the regions with the lowest atmospheric self-purification capacity are distributed in basins, whilst the regions with the highest atmospheric self-purification capacity are distributed in plateaus, plains, and islands ([PERSON], 2018) [1]. Some scholars focus on provinces and cities. For example, the spatial distribution of the atmospheric self-purification capacity index in Heilongjiang Province generally looks low in the north and high in the south ([PERSON] et al., 2020) [14].