Ozone layer on slow path to recovery

Carly Caramanna, a fifth grader at East Dover Elementary in Toms River, N.J., depicted 'Always Keep Sun Lotion Handy' in her contribution to the EPA Ozone Depletion Art Project

April 28, 1999
Web posted at: 11:45 AM EDT

The ozone layer is on a slow path to recovery, but continued reduction in ozone-depleting substances is needed to ensure a return to pre-ozone hole levels sometime in the middle of next century, according to the National Oceanic and Atmospheric Administration.

Reduced concentrations of methyl chloroform, a chemical previously used as a cleaning solvent, is primarily responsible for the three percent overall decline in ozone-depleting substances.

Since methyl chloroform is destroyed much more rapidly in the atmosphere by natural processes than are other ozone-depleting substances, it will diminish in the next five to 10 years to a level where it will cease to harm the ozone layer, said Stephen A. Montzka, a scientist at NOAA's Climate Monitoring and Diagnostics Laboratory in Boulder, Colo.

Thus, further reductions in the threat to the ozone layer must come from reductions in other ozone-depleting gases, Montzka and colleagues write in the April 22 issue of Nature.

Restrictions on the production of ozone-depleting chemicals imposed by the Montreal Protocol have resulted in a slight decrease in some harmful substances, such as certain chlorofluorocarbons. The global amount of a few chemicals continues to increase despite international regulation.

Levels of the most abundant and persistent chlorfluorcarbon, CFC-12, the bromine compound halon-1211 and hydrochlorofluorocarbons -- the chemicals used as replacements for CFCs -- continue to increase in the atmosphere.

Since halons are about 50 times more efficient at destroying ozone than the chlorine released by CFCs, continued increases of halon-1211, though very small, are slowing the collective decline of ozone-depleting chemicals in the atmosphere, sand Montzka.

"Emissions of halon-1211 have not decreased despite the ban on production in developed countries since 1994," said Montzka. Some of the continued release of this chemical results because a substantial reservoir exists in fire extinguishers that are still in use today in many developed countries.

Hydrochlorofluorocarbons are also increasing, but the scientists say they account for only about two percent of the ozone-depleting substances in the atmosphere.

"Progress toward reducing the threat to stratospheric ozone posed by CFCs and related gases is evident in measurements of air throughout the globe, and continuation of this trend would ensure the eventual recovery of the ozone layer," said Montzka.

"However, a sustained reduction of ozone-depleting agents will be realized only if use and release of these substances continues to decline."

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