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Since McDonald, at the beginning of this decade, first proposed that water vapor from SST exhaust would lead to increases in skin cancer, about a dozen man-induced mechanisms have been suggested as threatening to modify our stratospheric ozone uv-shield. Possible thinning of the ozone layer has been attributed to one or more of the catalytic ozone destroyers, water vapor (HO/sub x/), oxides of nitrogen (NO/sub x/), chlorine (ClX); or bromine (BrX). The original catalyst, HO/sub x/, rather quickly lost its role to NO/sub x/. In an almost unique evolution, computed sensitivity of stratospheric ozone to NO/sub x/ progressively declined until a reversal of effect occurred. Models now compute a thickening of the ozone layer for any but high level or very massive injections of NO/sub x/. Meanwhile, computed sensitivity to ClX has fluctuated widely and in 1978 models increased to the point where comparisons with observations were becoming an embarrassment. The potential role of BrX has also increased but awaits a credible source of stratospheric bromine to bring it center stage. More recently the atmospheric build-up of carbon dioxide, by cooling the stratosphere and increasing the chemical equilibrium level of ozone, has also been recognized as a potential modifier of the ozone layer.
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