Table 2.

Distribution of 1999 EPA ASPEN modeled estimates of benzene and 1,3-butadiene in ambient air in the eight-county study area (n = 886 census tracts).

	Benzene (μg/m3)	1,3-Butadiene (μg/m3)
Arithmetic mean	1.95	0.19
Geometric mean (95% CI)	1.72 (1.04–2.84)	0.14 (0.07–0.30)
Geometric SD	1.65	2.14
Minimum	0.42	0.01
Maximum	9.05	2.41
Percentile
25th	1.28	0.11
50th	1.72	0.16
75th	2.36	0.21
90th	3.18	0.31
99th	5.50	0.60