Crutzen, Paul Josef (1933-...), a Dutch chemist, discovered that certain compounds of nitrogen and oxygen break down ozone. Ozone, a form of oxygen in the earth's upper atmosphere, shields the earth from much of the sun's ultraviolet radiation. The ozone-destroying compounds are produced in automobile exhausts and in various industrial processes. Crutzen's work contributed to the realization in the 1970's that the earth's protective ozone layer is threatened by human activity, and the resulting environmental legislation that included laws concerning vehicle emissions. Crutzen shared the 1995 Nobel Prize for chemistry with American chemists Mario Molina and Frank Sherwood Rowland, who had studied the effects on the ozone layer of different substances, the chlorofluorocarbons (CFC's). See Molina, Mario Jose; Rowland, Frank Sherwood.