## 2 Theoretical Mechanism and Research Hypotheses
### The Effect of Atmospheric Self-Purification Capacity on the Governance of Environmental Pollution  
With the rapid development of the economy and society and the acceleration of urbanization, social activities aggravate the emission of pollutants aggravates, the environmental pollution intensifies, and the scope of pollution enlarges. When the emission of pollutants reaches the maximum allowable emission amount for the atmosphere of an ambient-air-protection target, it signals the environmental self-purification capacity of atmospheric pollutants [6]. In recent years, human activity, urban layout, industrial structure, and other factors have continuously increased the emission of environmental pollution, exacerbating air quality. Particularly, human factors change meteorological elements, further sustainably decrease atmospheric self-purification capacity, and aggravate environmental pollution. These cannot be ignored [25]. In terms of mechanism, the governance effect of regional atmospheric self-purification capacity on environmental pollution operates in three ways. First, factors such as temperature, near-surface wind speed, and precipitation affect the removal and accumulation of pollutants in local regions by changing the transport and diffusion capacities of the near-surface atmosphere [26; 27]. When the environment is polluted, it can gradually eliminate pollutants and achieve natural purification via physical, chemical, and biological actions. The dilution, diffusion, oxidation, and other physical or chemical actions of the atmosphere make the emitted pollutants appear. For example, particulate matter emitted into the atmosphere falls to the ground after being washed by rain and snow for atmospheric self-purification. Fully understanding and utilizing atmospheric self-purification capacity can reduce the concentration of pollutants and the harm of pollution. Second, the environmental bearing capacity sets a hard constraint for the formulation of the polices on the governance of environmental pollution. Therefore, the implementation of these policies should base itself on scientifically understanding the environmental self-purification capacity. Relevant parties determine the environmental bearing capacity, lay down corresponding operable policies on the treatment of environmental pollution, and control the concentration of environmental pollutants within the practical scope. The environmental policy serves as an important means to adjust industrial structure. For one region, it can achieve the goals of strengthening the environmental bearing capacity and of better adapting to the environmental bearing capacity by adjusting industrial structure and layout [28]. Third, atmospheric self-purification capacity reversely promotes urban green planning, and makes rational use of environmental resources to optimize urban planning and layout in line with regional features [5]. To enhance the atmospheric self-purification capacity, a region can enlarge the greening area, plant trees, and establish a nature reserve. Based on environmental improvement and protection, the ecological city that is people-oriented and suitable for human settlement will be built. In summary, this paper proposes research Hypothesis 1. **Hypothesis 1 (H1). **_Augmenting the environmental self-purification capacity helps to alleviate environmental pollution in one region._The Spatial Correlation Effect of Atmospheric Self-Purification Capacity on the Governance of Environmental Pollution  
The spatial effect of atmospheric self-purification capacity on environmental pollution depends on the view that environmental pollution in various regions has a spatial spillover effect. For example, whenever the PM2.5 concentration in neighboring regions increases, the PM2.5 concentration in one region will increase accordingly [29]. For atmospheric self-purification capacity under different meteorological conditions, the dilution and diffusion capacities of pollutants change.