Table 2.

Statistical descriptions of the NO${}_2$ concentration for the 19 stations (Unit: micrograms per cubic ($\mu$g/m${}^3$))

Station	Mean	Std.	Min	Max	Mann-Kendall	P-value	Theil-Sen’s	Trends
					seasonal statistical test		Slope Estimator
Station 1	56.44	17.09	15.36	143.03	−179	0.0 *	−10.51	Decreasing
Station 2	31.42	13.97	7.40	89.71	−165	0.0 *	−9.70	Decreasing
Station 3	27.89	14.86	3.92	80.07	−85	0.0 *	−5.17	Decreasing
Station 4	47.8	21.98	5.74	159.70	−11	0.6 *	−0.83	No trend
Station 5	32.31	15.56	8.85	96.67	55	0.00 *	2.51	Increasing
Station 6	29.7	12.17	6.23	64.51	−111	0.00 *	−5.19	Decreasing
Station 7	42.13	23.69	7.156	156.62	−127	0.00 *	−9.35	Decreasing
Station 8	15.73	6.72	3.44	47.79	−19	0.35 *	−0.74	No trend
Station 9	14.85	6.23	3.95	45.00	61	0.00 *	1.60	Increasing
Station 10	9.63	1.44	6.60	16.86	−60	0.00 *	−0.32	Decreasing
Station 11	21.68	9.01	6.64	61.11	15	0.47 *	0.41	No trend
Station 12	16.68	5.75	5.08	39.5	−113	0.00 *	−2.73	Decreasing
Station 14	33.79	21.05	2.36	109.13	−135	0.00 *	−7.50	Decreasing
Station 15	32.70	20.69	4.58	128.26	−181	0.0 *	−12.15	Decreasing
Station 16	47.86	19.68	11.2	119.31	−51	0.01 *	−3.40	Decreasing
Station 17	14.81	5.44	4.02	33.90	−103	0.00 *	−2.66	Decreasing
Station 18	21.27	10.02	2.97	79.31	−75	0.00 *	−2.88	Decreasing
Station 19	23.38	12.77	3.51	76.33	−71	0.00 *	−4.76	Decreasing
Station 20	8.60	2.94	2.77	22.53	−71	0.00 *	−1.18	Decreasing

${}^{\ast }$p<.05