**2. Study Area**

Taiyuan is the capital city of Shanxi Province in China (as shown in Figures 2 and 3). The terrain is surrounded by mountains in the east, west, and north. The central and southern part is the Fenhe River valley plain. The whole terrain is high in the north and low in the south, in the shape of a dustpan. Therefore, the average ground wind speed is small, the static wind frequency is high, and the precipitation is scarce, which is unfavourable to the city's diffusion of air pollutants.

**Figure 2.** Location of the study area in China.

As a typical resource-based city, Taiyuan has a special industrial structure. The industry is mainly heavy. Coal mining and combustion greatly impact the quality of the atmospheric environment. Taiyuan has also actively adjusted and upgraded its industrial structure for many years. As shown in Figure 4, the proportion of primary industry in Taiyuan is relatively small and in a downward trend, and the proportion of secondary industry and tertiary industry shows a "K" trend. After 2009, the tertiary industry became the leading industry in Taiyuan, basically maintaining a stable industrial pattern of "tertiary, secondary, and primary industry", reflecting the industrial structure characteristics of urbanisation. However, from 2013 to 2020, the air quality ranking of Taiyuan was always in the lower position of the environmental air quality ranking of national key cities. The poor atmospheric environmental quality has become an important factor restricting the development of Taiyuan.

**Figure 4.** Changes in the proportion of three industries in Taiyuan over the years.

#### **3. Methods and Data**

The coupling coordination model provides an intuitive measurement and evaluation of whether the system elements can interact and the overall coordinated development. The VAR model can measure the size and continuous influence of the interaction of elements between systems in the process of dynamic development. Referring to the practice of Liao et al. [27], this paper combines the two models to comprehensively analyse the coupling and internal mechanisms between atmospheric environmental quality and urban

industrial structure adjustment in Taiyuan from the perspectives of "static" and "dynamic". This section will specifically introduce the above models and the required data.
