NOx. such as nitric oxide, comes from many sources. It is a misconception that it is only the result of combustion devices. There are natural sources such as thunderstorms and ordinary plant life. Changes in agricultural practices could reduce soil emissions of the greenhouse gas nitrous oxide and the atmospheric pollutant nitric oxide, according to a new study by scientists at the University of California, Davis. “Agriculture is the main source of nitrous oxide globally, so this study is a starting point to help us understand how to manage and control it,” said UC Davis professor of soil biogeochemistry William Horwath, whose lab conducted the study.