*2.4. Environmental Management*

Environmental management in this study refers to the calculated emission intensity, environmental regulation intensity. The emission intensity is targeted at Xi'an, based on the ratio of the SO2, soot, and dust emissions to GDP. The environmental regulation intensity is targeted at Shaanxi province, based on the emissions and environmental investment.

The environmental regulation intensity is measured by environmental governance investment per unit of atmospheric pollutant emissions. The calculation formula is

$$ERI = Im\upsilon./Pollu.\tag{1}$$

where *ERI* represents the strength of environmental regulations; *Inv.* represents the investment in atmospheric environmental improvement; *Pollu.* represents the concentrations of atmospheric pollutants.

Environmental management datasets were obtained from the Statistical Yearbook (http://www.stats.gov.cn/, accessed on 6 May 2020), including the emission intensity (t/104 RMB) and the environmental regulation investment (108 RMB) in Xi'an, Shaanxi province.

#### *2.5. Statistical Analysis*

The Kolmogorov–Smirnov test was used to confirm that the datasets followed a normal distribution, and the analysis method was dependent on the results of the K-S test. Spearman correlation analysis was carried out between the concentrations of PM10 and PM2.5. Spearman correlation coefficients were also calculated for the relationships between atmospheric pollutants and the meteorological factors, environmental regulation intensity. One-way ANOVA and t-pair test were conducted to analyze differences at different monitoring sites and time scales (annual, seasonal, and monthly). All data analyses and figure drawings were performed in SPSS 20.0 and MATLAB R2019a.

#### **3. Results**
