Table 2.

Levels of the Ambient Exposures

Exposure	Window a	Mean	SD b	25th c	75th d	IQR e
PM2.5 (μg/m3)	1Wk	8.8	3.9	6.2	10.5	4.3
	4Wk	8.9	3.2	6.6	10.5	4.0
	8Wk	8.9	2.8	6.9	10.6	3.7
	1Yr	9.0	2.0	7.5	10.5	3.0
O3 (ppb)	1Wk	35.5	11.2	28.4	43.2	14.7
	4Wk	35.7	10.3	29.7	43.5	13.8
	8Wk	36.0	9.7	30.1	43.4	13.3
	1Yr	34.8	3.8	32.2	37.7	5.5
NO2 (ppb)	1Wk	21.6	10.6	12.7	28.9	16.2
	4Wk	21.4	10.1	12.9	29.2	16.3
	8Wk	21.4	9.8	13.3	29.1	15.9
	1Yr	22.3	8.1	16.3	27.8	11.6

^a1Wk, 4Wk, 8Wk and 1Yr means for the windows of 1 week, 4 weeks, 8 weeks and one year prior to the visit date;

^bSD is the standard deviation;

^c25^th is the 25^th percentile;

^d75^th is the 75^th percentile;

^eIQR is the interquartile range.