Stratospheric Levels of Chlorine to Peak by 2000

Newsbriefs

Stratospheric levels of chlorine should peak by the year 2000, according to the 14 June issue of

Global Environmental Change Report. Scientists at the National Oceanic and Atmospheric Administration in Boulder, Colorado, have been measuring levels of various CFCs and HCFCs in the lower atmosphere (troposphere) since 1991 and using those measurements to extrapolate stratospheric levels. (Chlorine in the stratosphere destroys ozone and permits higher levels of ultraviolet light to reach the Earth’s surface.) Tropospheric chlorine peaked in 1994 at 3,700 parts per trillion (ppt) and is now decreasing by about 25 ppt per year. The scientists predict that this will result in chlorine peaks in the stratosphere between 1997 and 1999.