Britannica Sources used in this answer

Why does ozone layer recovery take decades after CFC production is reduced?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

ozone depletion — Ozone depletion The Antarctic ozone hole reaches its maximum extent in October of each year. On October 7, 2021, when this image was captured, the Antarctic ozone hole spanned 24.8 million square km (9.6 million square miles).

The recovery of the ozone layer is a slow process primarily because of the long residence times of chlorofluorocarbons (CFCs) and other halocarbons in the atmosphere.21

Even after the production of these ozone-depleting chemicals was significantly reduced or phased out under the Montreal Protocol, the molecules already released remain in the stratosphere for decades. Once in the stratosphere, these compounds are broken down by ultraviolet radiation, which releases chlorine and bromine atoms that continue to destroy ozone molecules.234

Because these chemicals persist for such long periods, the reversal of ozone depletion is a gradual process. Furthermore, the rate of recovery is influenced by other changes in atmospheric composition, such as fluctuating levels of carbon dioxide, methane, and nitrous oxide, which can affect the chemical reactions involving ozone. Consequently, scientists estimate that it will take until the middle of the 21st century for ozone concentrations to return to 1980 levels.214