| Variable name | First-Tier and Second-Tier Cities | Other Cities |
| GMM | GMM | |
| City size | −0.803** | 2.294*** |
| (−2.26) | (2.95) | |
| Square of City Scale | 0.0531*** | −4.507*** |
| (2.64) | (−4.20) | |
| Environmental pollution | −43.78** | 2.171 |
| (−2.41) | (0.47) | |
| Interaction between urban scale and environmental pollution | 8.580** | −13.12 |
| (2.04) | (−0.36) | |
| Intercept term | 3.841*** | 2.754*** |
| (12.46) | (11.97) | |
| Control variable | Yes | Yes |
| Observation value | 2920 | 3097 |