Ozone Depletion and Its Consequences for the Fluence of CarcinogenicSunlight1

A slight reduction of the ozone level over the northern hemisphere in the period 1969-1986 has been reported (D. Lindley, Nature (Lond.), 323: 293, 1988). Ozone measurements performed in Oslo are in agree ment with this. However, the ozone level for 1987 and 1988 was above normal, and no negative or positive trend is apparent for the last 10 years. The consequences of an ozone reduction for the fluence rate of carcinogenically effective sunlight was evaluated on the basis of recent action spectra for mutagenesis in cells, carcinogenesis in mice, and erythema induction in humans. Depending on the choice of action spec trum we find amplification factors (defined as percentage increase in yearly fluence of carcinogenically efficient sunlight per percentage reduc tion of the ozone level) between 1.1 and 1.3 at latitudes between 0 and 20° and between 0.9 and 1.1 for Northern Europe. These estimates are significantly lower than 2.0, which is the value found when the calcula tions are based on the DNA absorption spectrum (R. B. Setlow, Proc. Nati. Acad. Sci. USA, 71: 3363-3366,1974).