Table 7.

Correlation with the second-level air standard.

Correlation coefficient and correlation degree	ζ1	ζ2	ζ3	ζ4	ζ5	R2
$S_1^{\prime }$	1.000	0.832	0.333	0.646	0.431	0.648
$S_2^{\prime }$	1.000	0.716	0.333	0.591	0.405	0.609
$S_3^{\prime }$	1.000	0.775	0.536	0.743	0.333	0.677