Implications of different approaches for characterizing ambient air pollutant concentrations within the urban airshed for time-series studies and health benefits analyses

Table 1 Descriptive statistics of ambient air pollutant concentrations in metropolitan Atlanta during May through October.^a

Pollutant	Number of Monitors	Number of Observations	Central monitor Mean (IQR)	Unweighted average Mean (IQR)	Population-weighted average Mean (IQR)
8-h ozone, ppb^b	5	2205	56.7 (26.4)	54.8 (25.0)	55.3 (22.6)
24-h PM₁₀, μg/m^3c	9	1563	29.4 (13.4)	29.7 (14.0)	27.4 (12.4)
24-h PM_2.5, μg/m^3d	11	1134	19.2 (9.8)	19.9 (9.1)	18.4 (8.7)
24-h PM_2.5 sulfate, μg/m^3d	6	980	6.3 (3.7)	5.8 (3.6)	5.8 (3.5)
24-h PM_2.5 organic carbon, μg/m^3d	6	1089	4.19 (1.92)	4.60 (2.45)	4.71 (2.71)
24-h PM_2.5 elemental carbon, μg/m^3d	6	1089	1.62 (0.91)	1.25 (0.68)	0.82 (0.53)
1-h nitrogen dioxide, ppb^b	6	2190	42.0 (19.7)	27.7 (13.5)	22.0 (10.1)
1-h carbon monoxide, ppm^b	3	1999	1.45 (0.83)	1.39 (0.92)	0.87 (0.46)
1-h sulfur dioxide, ppb^b	5	2201	13.9 (13.0)	10.2 (7.7)	9.6 (7.6)

Abbreviations: interquartile range (IQR), hour (h), parts per billion (ppb), micrograms per cubic meter (μg/m³), parts per million (ppm).
^aAmbient air pollutant concentrations are presented as three-day moving averages.
^bData begin on May 1, 1993.
^cData begin on May 1, 1996.
^dData begin on August 1, 1998.

ISSN: 1476-069X