Table 2.

The year-on-year comparison of monthly mean ± SD of air pollution in March.

Year	2017	2018	2019	2020
PM2.5 (μg/m3)	34.23±9.72	28.65±15.54	37.37±23.95	20.39±6.31
p-value	(ref)	0.093	0.521	<0.001
		(ref)	0.140	0.006
			(ref)	<0.001
PM10 (μg/m3)	54.67±11.87	46.73±21.71	60.77±31.05	39.16±7.23
p-value	(ref)	0.083	0.346	<0.001
		(ref)	0.072	0.085
			(ref)	0.001
NO2 (ppb)	23.61±6.16	20.31±5.26	20.38±6.63	16.22±4.95
p-value	(ref)	0.041	0.060	<0.001
		(ref)	0.970	0.002
			(ref)	0.008
CO (ppm)	0.536±0.074	0.495±0.093	0.513±0.134	0.387±0.040
p-value	(ref)	0.060	0.353	<0.001
		(ref)	0.578	<0.001
			(ref)	<0.001

All values present mean ± SD of all daily concentrations per each month.

Paired t-test was used for comparison of PM_2.5, PM₁₀, NO₂, and CO levels on the same day in the current year versus each prior year.