Table 1. Descriptive statistics of the concentrations of pollutants.

Pollutant	Unit	data category	N a	Mean	SD	Min	25%	Median	75%	Max
Indoor PM 2.5	μg/m3	hourly	792	44	35	4	15	34	63	193
		daily average	33	44	28	9	22	36	65	119
Ambient PM 2.5	μg/m3	hourly	792	69	49	3	30	58	96	280
		daily average	33	69	38	15	36	62	91	165
I/A (PM 2.5 )		hourly	792	0.63	0.27	0.12	0.48	0.6	0.74	3.3
		daily average	33	0.63	0.15	0.31	0.54	0.62	0.73	0.98
O 3	μg/m3	hourly	825	78	67	1	14	67	121	285
		daily average	35	76	30	18	54	77	104	123
NO 2	μg/m3	hourly	816	51	25	8	31	47	68	143
		daily average	34	52	13	17	41	52	61	76
SO 2	μg/m3	hourly	825	7	6	1	3	6	9	60
		daily average	35	8	4	3	5	7	9	19

a. Valid ambient and indoor PM_2.5 mass concentrations were simultaneously available for 33 residences.