The potential destruction of the ozone layer by nuclear war poses grave dangers to humanity and ecosystems. In addition to direct effects on surface climate, previous studies of regional scale nuclear exchanges and associated fires have considered how injection of reactive nitrogen and smoke heating could deplete stratospheric ozone. However, studies of urban fires provide evidence for substantial emissions of chlorine, bromine and possibly iodine compounds (for example, from the burning of plastics, flame retardants, home insulation, medical materials, etc.). We propose to evaluate how much these potent ozone-destroying chemicals would add to current estimates of ozone loss following nuclear exchanges. Further, new studies in our group have altered the fundamental understanding of atmospheric chemistry impacts of fire smoke, and are highly likely to increase expected stratospheric ozone losses following nuclear war from these emissions. We have shown that greatly enhanced solubility of hydrochloric acid in oxidized organic smoke particles enhances chlorine-catalyzed ozone destruction. While the Antarctic ozone hole is currently slated to recover by the 2060s, we will probe the extent to which a nuclear exchange could not only bring it back but make it global, i.e., reversing one of humanity's great environmental achievements and driving widespread devastation.