| Carbon | Nitrogen | PM-10 | Sulfur | |||
| Year | monoxide | Lead | dioxide | Ozone | particulates | dioxide |
| ppm | ug/m3 | ppm | ppm | ug/m3 | ppm | |
| (251 sites) | (184 sites) | (127 sites) | (401 sites) | na | (389 sites) | |
| 1979 | 9.1 | 0.97 | 0.024 | 0.133 | na | 0.0113 |
| 1980 | 8.5 | 0.77 | 0.024 | 0.135 | na | 0.0105 |
| 1981 | 8.2 | 0.61 | 0.023 | 0.125 | na | 0.0102 |
| 1982 | 7.8 | 0.55 | 0.022 | 0.123 | na | 0.0093 |
| 1983 | 7.7 | 0.41 | 0.022 | 0.136 | na | 0.0090 |
| 1984 | 7.7 | 0.37 | 0.023 | 0.123 | na | 0.0092 |
| 1985 | 7.0 | 0.24 | 0.022 | 0.122 | na | 0.0086 |
| 1986 | 7.0 | 0.15 | 0.022 | 0.118 | na | 0.0084 |
| 1987 | 6.6 | 0.12 | 0.022 | 0.124 | na | 0.0082 |
| 1988 | 6.5 | 0.11 | 0.022 | 0.135 | na | 0.0083 |
| (363 sites) | (189 sites) | (225 sites) | (661 sites) | (934 sites) | (486 sites) | |
| 1989 | 6.2 | 0.09 | 0.021 | 0.114 | 31.7 | 0.0087 |
| 1990 | 5.8 | 0.09 | 0.020 | 0.112 | 29.4 | 0.0082 |
| 1991 | 5.6 | 0.07 | 0.020 | 0.113 | 29.1 | 0.0079 |
| 1992 | 5.2 | 0.06 | 0.019 | 0.105 | 26.8 | 0.0074 |
| 1993 | 4.9 | 0.05 | 0.019 | 0.108 | 26.0 | 0.0072 |
| 1994 | 5.1 | 0.05 | 0.020 | 0.107 | 26.0 | 0.0070 |
| 1995 | 4.5 | 0.04 | 0.019 | 0.112 | 24.9 | 0.0057 |
| 1996 | 4.2 | 0.04 | 0.019 | 0.106 | 23.9 | 0.0056 |
| 1997 | 3.9 | 0.04 | 0.018 | 0.105 | 23.8 | 0.0054 |
| 1998 | 3.8 | 0.04 | 0.018 | 0.110 | 23.7 | 0.0053 |
Source: U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, National Air Quality and Emissions Trends Report, 1998, Table A-9 (EPA, OAQPS, Research Triangle Park, NC, 2000).
Notes: ppm = parts per million. ug/m3 = micrograms per cubic meter. na = not available. Sulfur dioxide and nitrogen dioxide records are annual arithmetic means, Carbon monoxide records are arithmetic means of second maximum non-overlapping 8-hour concentrations. Ozone records are arithmetic means of second daily maximum 1-hour concentrations. Lead records are arithmetic means of maximum quarterly measurements. PM-10 records are weighted annual arithmetic means. The National Ambient Air Quality Standards for these pollutants are as follows: sulfur dioxide, 0.03 ppm; carbon monoxide, 9 ppm; ozone, 0.12 ppm; nitrogen dioxide, 0.053 ppm; PM-10, 50 ug/m3; and lead, 1.5 ug/m3.
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