Stratospheric ozone in the 21st Century: The chlorofluorocarbon problem

Ozone (O3) exists in a dynamic equilibrium in the stratosphere, balanced between formation by solar ultraviolet photolysis (λ < 242 nm) of molecular O2 (O + O2 → O3) and destruction by various chemical processes including several chain reaction sequences triggered by HOx, NOx, and ClOx radicals. The ozone dissipates over Antarctica by November through northward mixing, only to begin reappearing in late August of the following year. Substantial ozone losses have also appeared, although not as spectacularly as over Antarctica, in the Northern Hemisphere's temperate and polar regions. The primary cause for the Antarctic ozone loss, and the probable cause for the northern losses, is the increasing concentration in the stratosphere of anthropogenic chlorine, especially chlorine released by solar UV photolysis from chlorofluorocarbon (CFC) compounds such as CCl2F2 (CFC-12), CCl3F (CFC-11) and CCl2FCClF2 (CFC-113). Because these molecules have average atmospheric lifetimes of many decades, excess anthropogenic chlorine will persist in the stratosphere for comparable time periods, and the Antarctic ozone hole will be an important atmospheric phenomenon throughout the 21st century