Current and Future Levels of Chlorine in the Stratosphere
Source: World Meteorological Organization, Scientific Assessment of Ozone Depletion: 2002, WMO Global Ozone Research and Monitoring Project - Report No. 47, Geneva, 2002.
Plotted above are the levels of total effective stratospheric chlorine (top) and levels of some important individual chlorofluorocarbons (CFCs) (bottom) that were phased out in industrialized countries in 1995 by the Montreal Protocol. Since both chlorine and bromine act to destroy ozone, but bromine acts about 45 times more effectively to do so, levels of "effective stratospheric chlorine" are arrived at by converting the bromine to amount of chlorine that would destroy and equivalent amount of ozone. These observations show that the amount of effective stratospheric chlorine rose steadily until the mid-1990's, then began to level out and slowly drop when controls on the emissions of CFCs and other ozone-depleting substance kicked in. Since chlorine levels are starting to drop in the stratosphere, the ozone layer should start to recover in the next few years. However, it takes many decades for natural processes to remove CFCs from the atmosphere, and it will take many decades for the ozone layer to recover.