Ozone Layer Over U.S. Shows Record Thinning

The protective ozone layer above the United States thinned at a record rate earlier this year, reaching concentrations as much as 18% less than average readings since the 1960s, a university researcher reported Thursday.

Walter Komhyr of the University of Colorado said ground instruments at five sites in the United States detected the thinning ozone during January, February and March.

At an instrument in Boulder, Colo., for instance, the February reading was 298 Dobson units, the lowest at that station since 1967. At Wallops Island, Va., the reading was 289 Dobson units, the lowest since 1970 at that location, Komhyr said.

Ozone in the upper atmosphere filters ultraviolet rays from sunlight, preventing the damaging radiation from reaching Earth’s surface. The ozone is believed to be thinning because of industrial chemicals, principally chlorofluorocarbons, or CFCs, that were widely used as cleaning solvents and refrigerants.