Table 3

Statistics of the air quality variables (annual means unless otherwise noted)

Period	Species	Mean	SD	Counties
*Glass-fibre filters; †estimated values; ‡teflon filters; §counties with IPN PM_2.5 data.
VMTG and VMTD, vehicle miles travelled by gasoline and diesel powered vehicles.
Particulate matter (μg/m³):
1960–64	TSP	96.92	41.81	281
1970–74	TSP	69.65	28.37	1258
1979–81	TSP	60.51	19.63	1277
1989–91	TSP	48.78	16.28	592
1979–84	PM₁₅	38.30	10.73	101
1995–97	PM₁₀	28.64	8.05	648
1999	PM₁₀	23.26	6.73	675
1979–84	PM_2.5	19.19	5.66	101
1999	PM_2.5	12.97	3.74	540
Sulfate aerosol (μg/m³):
1960–64	SO₄²⁻*	9.92	5.36	193
1970–74	SO₄²⁻*	9.31	3.77	294
1979–81	SO₄²⁻*	9.07	3.77	329
1982–88	SO₄²⁻*	7.34	3.88	216
1982–88	SO₄²⁻†	7.55	3.39	425
1989–96	SO₄²⁻†	5.85	3.18	425
1979–84	SO₄²⁻‡	5.26	2.70	79
Sulfur dioxide (ppb):
1960–69	SO₂	56.63	48.42	42
1970–74	SO₂	16.18	14.62	279
1979–81	SO₂	9.04	5.65	480
1989–91	SO₂	7.20	4.13	411
1995–97	SO₂	4.94	2.69	393
95th percentile CO (ppm):
1960–69	CO	13.81	8.47	44
1970–74	CO	9.64	5.63	206
1979–81	CO	5.90	3.54	272
1989–91	CO	2.69	1.22	246
1995–97	CO	1.72	0.76	261
Nitrogen dioxide (ppb):
1960–69	NO₂	35.76	11.22	33
1970–74	NO₂	28.11	12.62	151
1979–81	NO₂	20.06	10.22	236
1989–91	NO₂	18.02	8.43	194
1995–97	NO₂	15.43	7.35	240
95th percentile O₃(ppb):
1970–74	O₃	146.99	51.63	156
1979–81	O₃	120.12	36.30	452
1989–91	O₃	84.71	14.77	439
1995–97	O₃	73.18	10.01	520
Vehicle-miles travelled/sq mile:
1985–97	VMTG	1.84	9.20	3084
1985–97	VMTG	20.21	37.70	99§
1985–97	VMTD	0.12	43.00	3084
1985–97	VMTD	0.98	1.75	99§