Table A-9. National Long-Term Air Quality Trends, 1979-1998 CO Pb NO2 Ozone PM10 SO2 Year 2nd Max. 8-h Max. Qtr. Arith. Mean 2nd Max. 1-hWtd. Arith. MArith. Mean ppm µg/m3 ppm ppm µg/m3 ppm 1979-88(251 sites) (184 sites) (127 sites) (401 sites) - (389 sites) 1979 9.1 0.97 0.024 0.133 - 0.0113 1980 8.5 0.77 0.024 0.135 - 0.0105 1981 8.2 0.61 0.023 0.125 - 0.0102 1982 7.8 0.55 0.022 0.123 - 0.0093 1983 7.7 0.41 0.022 0.136 - 0.0090 1984 7.7 0.37 0.023 0.123 - 0.0092 1985 7.0 0.24 0.022 0.122 - 0.0086 1986 7.0 0.15 0.022 0.118 - 0.0084 1987 6.6 0.12 0.022 0.124 - 0.0082 1988 6.5 0.11 0.022 0.135 - 0.0083 1989-98(363 sites) (189 sites) (225 sites) (661 sites) (934 sites) (483 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