gaseous form of oxygen that constitutes less than one part per million of the gases in the atmosphere, yet absorbs most of the ultraviolet radiation which has been proven to be harmful to humans as well as other life forms on Earth
EESiFlo North America, Terminology and Glossary: Meteorological Weather Station Terms, Pennsylvania, USA 2002, flowmeterdirectory.com/flowmeter_terminology, (Wthr - Amer) {554}