Table 6.

Heterogeneity analysis results.

Variable	Eastern China	Northeastern China	Central China	Western China
	zPM	zPM	zPM	zPM
zln(SO2)	1.011***−6.21	1.536*** −6.29	0.560*−1.96	0.745*** −4.6
zln(PGDP)	−0.594*** (−3.56)	−0.462*** (−4.13)	−0.615*** (−3.78)	−0.717*** (−4.18)
zNHP	−0.036 (−0.99)	−0.663** (−2.53)	0.532***−2.75	0.31 −1.64
zPMHS	0.013 −0.81	−0.016 (−0.61)	0.016 −0.52	0.004 −0.12
zln(PDI)	0.038 −0.34	0.028 −0.8	−0.018 (−0.48)	−1.141*** (−6.37)
zUR	−0.821*** (−5.85)	−1.156*** (−4.14)	−0.892** (−2.48)	1.083* −1.7
zPAR	0.957***−3.6	0.936 −1.12	−0.524 (−0.38)	−0.006 (−0.33)
_cons	0.486***−5.01	0.089 −0.6	−0.887*** (−8.83)	0.891*** −2.93
N	120	36	72	132
R 2	0.855	0.947	0.856	0.848
F-statistic	102.375***	90.985***	62.226***	107.195***

t-statistics in parentheses.

^*p < 0.1,

^**p < 0.05,

^***p < 0.01.