United Press International: The National Oceanic and Atmospheric Administration says nitrous oxide has become Earth’s largest ozone-depleting substance emitted through human activities. NOAA scientists said they have, for the first time, evaluated nitrous oxide emissions in terms of their potential impact on Earth’s ozone layer. Not only did they find nitrous oxide to be the top ozone-depleting substance, but they said they expect it to remain so throughout the 21st century. The scientists said nitrous …