The principal mission of Atmospheric Chemistry and Dynamics is to understand the behavior of stratospheric ozone and trace gases that influence ozone. Ozone and trace gases such as methane, nitrous oxide, and the chlorofluorocarbons profoundly influence the habitability of the Earth even though together they comprise less than one percent of the Earth's atmosphere. Ozone itself absorbs nearly all the biologically damaging solar ultraviolet radiation before it reaches the Earth's surface. The Clean Air Act of 1977 assigns the responsibility for studying the ozone layer to NASA. Atmospheric Chemistry and Dynamics is the center for ozone and related atmospheric research at the Goddard Space Flight Center.