YEAR NUMBER CONC 1938 200 120.6 1941 22 107 1943 25 66.9 1944 50 85.7 1945 100 134 1947 50 103.2 1949 49 145 1950 100 100.7 1951 1000 107 1956 21 135 1963 100 110 1964 50 96.6 1969 13 48.4 1971 29 85.9 1971 100 74.4 1972 79 60 1974 386 48 1975 1300 79 1976 13 83.2 1977 7 52.7 1978 66 51.4 1978 12 89.5 1979 33 100.2 1979 21 131 1979 14 104.3 1979 185 67.6 1980 50 61.4 1981 53 71.2 1981 51 89 1982 89 115 1982 20 78 1982 90 76 1983 4435 66 1983 22 60.3 1983 38 78.3 1983 63 99.1 1983 809 102.9 1984 1500 65 1984 119 83.9 1984 114 72 1984 9 58.9 1984 36 59 1985 12 102 1985 1239 83 1986 20 65 1986 12 68 1986 100 54.7 1987 307 52.9 1987 120 66.9 1988 36 62.4 1988 14 70.3 1988 28 86.6 1988 40 78.6 1988 49 73 1988 20 60.7 1989 12 103.7 1989 15 64.5 1989 104 91.3 1989 1222 77.7 1989 20 87.9 1990 54 58.6