## 3 Results and Discussions
### Spatial Distribution Characteristics of PM\({}_{2.5}\) in Chenzhou City
The valley terrain of northwest Yongxing County, Anren County, and the southwestern region of Guiyang County--situated in the epicenter of the southward dust transmission from northern regions--remains particularly vulnerable to dust influx from transmission channels emanating from Xi'an, Linfen, Lanzhou, and Jiouan. Evaluating the seasonal spatial distribution patterns of PM\({}_{2.5}\) in Chenzhou City, as illustrated in Figure 6, reveals that during spring, concentrations predominantly range between 12.45 and 42.26 \(\mathrm{\SIUnitSymbolMicro m}^{-3}\). Notably, regions of elevated concentration manifest in the northwestern sectors of Suvian and Beihu Districts, as well as in the southwestern expanse of Yongxing County and the northeastern sector of Guiyang County. Contrasting these findings with the annual average spatial distribution, there is a discernible reduction in pollutant concentration across the southern and eastern precincts of Chenzhou City during the spring season. With the conclusion of the heating season in March, local emissions in Chenzhou City witnessed a relative decline, particularly in the vicinity of the city itself. The diminished coal combustion in the surrounding counties, districts, and townships during spring likely correlates with the observed reduction in pollutant concentrations in the outskirts of Chenzhou City. During the summer months, the PM2.5 pollution levels in Chenzhou City consistently remain beneath the national first-tier limit standard. Nonetheless, isolated pockets of heightened PM2.5 concentrations, particularly in Jiahe County and the northwestern region of Guiyang County, escalate to 32.60 ug\(\cdot\)m\({}^{-3}\), marginally exceeding the established standard. Such elevations could potentially be ascribed to pollutant discharges stemming from coal mining activities and industrial precincts within Jiahe County. The broader PM2.5 pollution during the summer season often manifests in a milder form, a consequence of increased temperatures that intensify the convective tendencies of atmospheric circulation. Additionally, the prevalence of southerly winds during summer months facilitates the swift dispersion of pollutants. During the autumn season, the concentration of PM2.5 ranges between 31.27 and 53.08 ug\(\cdot\)m\({}^{-3}\). In contrast to spring and summer, the severity of PM2.5 pollution markedly escalates during autumn. Regions previously characterized by low PM2.5 values in spring transition to high-concentration zones in the autumn months, notably in the northern and western sectors. As expounded in Section 3.3, atmospheric trajectories following holiday periods demonstrate that air masses imbued with pollutants, originating from northeastern  
Figure 6: Seasonal variations in the spatial distribution of PM2.5 in Chenzhou City (**(a)** PM2.5 spatial distribution (spring) (**b**) PM2.5 spatial distribution (Summer) (**c**) PM2.5 spatial distribution (Autumn) (**d**) PM2.5 spatial distribution (Winter) (note: the illustration was crafted utilizing ArcGIS software, specifically version 10.2. For further reference, please visit the following URL. : [[https://www.arcgis.com/index.html](https://www.arcgis.com/index.html)]([https://www.arcgis.com/index.html](https://www.arcgis.com/index.html)) (accessed on 16 October 2023)). Guangxi and northeastern Hunan--including locales such as Changsha, Yueyang, and Yiyang--converge with local emission sources during the autumn season. The northwestern region of Chenzhou City is distinguished by its undulating terrain, with the Dongjiang Lake Scenic Area nestled amidst the imposing Bamian and Zhuguang Mountains. The geographical impediments presented by the Bamian and Zhuguang Mountains in this northwestern sector of Chenzhou obstruct the free dispersion of pollutants, leading to their accumulation. The spatial distribution of PM\({}_{2.5}\) during winter closely mirrors the annual average.