Arctic Ozone Hole and Enhanced Mid‐Latitude Ozone Losses Due To Heterogeneous Halogen Chemistry Following a Regional Nuclear Conflict

Abstract In a global‐scale nuclear war, massive explosions, intense heat, and radioactive fallout would cause extensive harm to humanity and ecosystems. Further, previous studies of even regional‐scale nuclear conflicts show that the smoke from large‐scale fires caused by such weapons could lead to global‐scale ozone loss. However, combustion studies show that urban fires release key ozone‐depleting substances that were not previously considered in nuclear war studies, particularly chlorine and bromine compounds. Recent wildfire studies have also shown that high solubility of hydrochloric acid in oxidized organic smoke particles can greatly enhance chlorine‐driven ozone loss. For the first time, here we simulate the impacts of a nuclear war on the ozone layer using a chemistry‐climate model that accounts for fire‐related halogen emissions as well as HCl solubility and heterogeneous chemistry in smoke particles. Our results show that a regional war scenario with 5 Tg of soot could result in a ∼40% reduction in the global ozone burden, nearly twice as much as previous studies. The calculated ozone losses exceed ∼80% over the Arctic, comparable to those observed when the Antarctic ozone hole was discovered and hence represent an Arctic ozone hole. Ozone losses also reach ∼50% over mid‐latitudes in the Northern Hemisphere, including highly populated areas. The enhanced ozone loss compared to previous studies is attributable to combined non‐linear effects from the incorporation of halogen emissions and updated heterogeneous chemistry in smoke particles. Such ozone losses lead to a large increase in surface ultraviolet exposure, posing grave risks to humanity and ecosystems.