By Sid Perkins
Chemical analyses of Earth’s lower atmosphere show that the overall concentration of bromine, a component of many potent ozone-destroying chemicals, has dropped about 5 percent since reaching a peak in 1998. Besides being a promising sign for Earth’s beleaguered ozone layer, the decline validates the decision by many countries to regulate the production and use of the predominant bromine-releasing compound, some scientists say.
Half the bromine that makes its way into the upper layers of the atmosphere comes from methyl bromide, says Stephen A. Montzka of the National Oceanic and Atmospheric Administration’s Climate Monitoring and Diagnostics Laboratory in Boulder, Colo. Much production and use of that chemical, often as an agricultural fumigant, is being phased out under the Montreal Protocol on Substances that Deplete the Ozone Layer as amended in 1997.