Nitrogen dioxide
From Glossary of Meteorology
nitrogen dioxide
A brown gas, formula NO2, found at all levels in the atmosphere.
In the troposphere it photodissociates to give free oxygen atoms, which then form ozone, and is thus a key player in local and regional air pollution events. In the stratosphere it participates in catalytic ozone destruction cycles, but also forms stable nitrate reservoir species that ameliorate ozone loss.
