Table 1.

The regression results between PM_2.5 concentrations and GDP per capita at the city and provincial levels in 2013, 2017, and 2020, respectively.

Variables	GDP per capita at the city level			GDP per capita at the provincial level
	2013	2017	2020	2013	2017	2020
Intercept	48.79∗∗	32.00∗∗	25.67∗∗	42.04∗	32.48∗∗	24.61∗∗
β1	4.04∗∗	2.54∗∗	1.38∗∗	5.09	1.86	1.28
β2	−0.21∗∗	−0.11∗∗	−0.05∗∗	−0.20	−0.05	−0.03

β₁ denotes the coefficient of GDP per capita values; β₂ denotes the coefficient of the square of GDP per capita values. ∗∗ is statistical significance at the 5% level; ∗ is statistical significance at the 10% level.