Variable name	First-Tier and Second-Tier Cities		Other Cities
Variable name	2SLS	GMM	2SLS	GMM
City size	−0.496**	−0.496**	0.738*	0.738*
City size	(−2.10)	(−2.23)	(1.67)	(1.66)
Square of City Scale	0.0307**	0.0307**	−2.020***	−2.020***
Square of City Scale	(2.28)	(2.45)	(−3.17)	(−3.02)
Environmental pollution	−28.46**	−28.46**	−1.478	−1.478
Environmental pollution	(−2.47)	(−2.52)	(−0.61)	(−0.60)
Interaction between urban scale and environmental pollution	5.858**	5.858**	16.78	16.78
Interaction between urban scale and environmental pollution	(2.17)	(2.23)	(0.86)	(0.84)
Intercept term	0.731***	0.731***	0.249*	0.249*
Intercept term	(3.62)	(3.66)	(1.77)	(1.77)
Control variable	Yes	Yes	Yes	Yes
Observation value	2920	2920	3097	3097