Table 3. Mean and within-day standard deviation (std_wd) of meteorological and air pollutant factors, averaged over specific hospital-days stratified by temperature (T) and air pressure (AP).

		high T (>26 °C)		mild T (21–26 °C)		low T (<21 °C)		p value!
		low AP (<1009 hpa)	high AP (≥1009 hpa)	low AP	high AP	low AP	high AP
Number of hospital-days		6288	748	2274	3021	164	6537	‒
RH	Mean	73.54 ± 6.47	75.61 ± 4.55	73.47 ± 10.18	72.97 ± 8.21	79.05 ± 6.38	72.2 ± 9.89	<0.001
	stdwd	8.71	8.78	8.8	8.94	7.23	8.21
CO	Mean	0.48 ± 0.24	0.6 ± 0.25	0.58 ± 0.27	0.62 ± 0.26	0.57 ± 0.26	0.65 ± 0.46	<0.001
	stdwd	0.25	0.29	0.27	0.3	0.22	0.3
NO2	Mean	15.92 ± 7.2	19.08 ± 7.62	20.51 ± 8.27	22.19 ± 8.48	20.18 ± 8.58	22.12 ± 8.2	<0.001
	stdwd	7.06	8.07	8.79	9.25	8.68	9.08
PM10	Mean	50.06 ± 22.44	71.48 ± 31.3	64.24 ± 30.96	72.51 ± 41.43	56.19 ± 33.36	66.69 ± 34.72	<0.001
	stdwd	14.81	21.48	22.74	22.41	20.24	22.17
PM2.5	Mean	29.57 ± 13.9	41.18 ± 19.25	37.08 ± 17.14	40.28 ± 21.51	35.1 ± 22.29	37.19 ± 18.62	<0.001
	stdwd	9.51	12.64	12.55	12.55	12.96	12.15
SO2	Mean	4.25 ± 2.07	5.16 ± 2.32	3.92 ± 1.91	4.58 ± 2.6	3.03 ± 1.48	4.12 ± 2.13	<0.001
	stdwd	2.57	2.99	2.06	2.44	1.56	1.96
O3	Mean	27.88 ± 12.71	33.54 ± 11.16	33.6 ± 13.08	32.02 ± 10.67	27.48 ± 8.53	25.92 ± 9.09	<0.001
	stdwd	16.95	21.56	17.12	17.98	13.07	13.16
T	Mean	28.87 ± 1.46	27.24 ± 0.8	24.34 ± 1.26	23.04 ± 1.45	19.53 ± 1.13	17.59 ± 2.45	<0.001
	stdwd	1.97	2	2.09	2.14	1.69	2.01

The std_wd was estimated by the hourly measurement of each day.

!: Across-strata comparison: one-way ANOVA for age and BMI, and chi-square test for gender and comorbidity proportions.