. Author manuscript; available in PMC: 2013 Aug 14.

Published in final edited form as: J Expo Sci Environ Epidemiol. 2009 Sep 16;21(1):10–19. doi: 10.1038/jes.2009.49

Table 1.

Descriptive statistics for air pollution data

						Percentiles

Pollutant	N^a	Time period	Metric	Mean	SD	25th	50th	75th	Max
CO (ppm)	3486	1/1/1993-6/30/2003	1-hr max	1.6	1.1	0.8	1.3	2.2	7.7
			24-hr average	0.7	0.4	0.5	0.6	0.9	3.7
			Commute (7–10am, 4–7pm)	0.7	0.4	0.4	0.6	0.9	4.0
			Day-time (8am–7pm)	0.5	0.3	0.4	0.5	0.7	2.6
			Night-time (12am–6am)	0.8	0.7	0.3	0.5	1.0	5.2

NO₂ (ppb)	3635	3/1/1994-12/31/2004	1-hr max	43	18	30	41	53	181
			24-hr average	22	10	15	21	28	74
			Commute (7–10am, 4–7pm)	21	11	13	20	27	97
			Day-time (8am–7pm)	17	9	10	16	22	82
			Night-time (12am–6am)	25	16	13	22	35	97

O₃ (ppb)	2883	March-October, 1993–2004	8-hr max	53	22	38	51	67	148
			1-hr max	62	25	45	59	76	180
			24-hr average	30	12	21	29	37	81
			Commute (7–10am, 4–7pm)	35	16	24	35	45	106
			Day-time (8am–7pm)	45	20	32	44	58	123
			Night-time (12am–6am)	14	12	3	11	22	64

PM_2.5 (µg/m³)	1660	8/1/1998-12/31/2004	1-hr max	29	16	18	26	36	188
			24-hr average	16	9	10	14	21	72
			Commute (7–10am, 4–7pm)	17	9	10	15	21	76
			Day-time (8am–7pm)	15	8	8	13	19	71
			Night-time (12am–6am)	17	11	5	9	14	88

Number of days used in analysis

PM_2.5 was measured continuously using a tapered element oscillating microbalance (TEOM) operated at 30°C to minimize volatilization. Gaseous pollutants were measured using standard approaches (NO₂ and O₃ by chemiluminescence and CO by infrared analyzer).