*4.1. Descriptive Statistics*

The original data of various indicators of the Taiyuan atmospheric environment system and the industrial system can be obtained from the official website of the Taiyuan Bureau of Statistics. Among them, the number of days with air quality above grade II, the upgrading of the industrial structure, and the total investment in fixed assets include the data for 20 years, from 2001 to 2020. Industrial sulphur dioxide emission, industrial smoke (powder) dust emission, and the comprehensive utilisation rate of general industrial solid waste cover 15 years of data, from 2003 to 2017. The data of industrial structure rationalisation include the data for 16 years, from 2003 to 2018, as shown in Table 4. Considering the amount of information and availability of data, this paper finally selected the data from 2003 to 2017 for empirical analysis. Due to the different dimensions of the above data, the range method was used to standardise the above data. According to the positives and negatives of the index, we used Formulas (1) and (2) to deal with it, respectively. The results are shown in Table 5.

