It’s easy to confuse the three gases: nitric oxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O). Here are some definitions:
nitric oxide—A colorless gas, formula NO, the most common form of nitrogen emitted into the atmosphere, either by fuel combustion or due to natural emissions.
Nitric oxide is interconverted with nitrogen dioxide fairly readily in the atmosphere, resulting in catalytic cycles leading to ozone formation in the troposphere and ozone loss in the stratosphere.
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.
nitrous oxide—Colorless gas, formula N2O, released by bacterial activity at the earth’s surface.
It has an atmospheric lifetime of about 160 years and is currently present at a level of about 330 ppb. Its atmospheric significance is that it is transported into the stratosphere, where its reaction with excited oxygen atoms (O1D) is the major source of active nitrogen; it is also a major greenhouse gas. In large amounts, it has anesthetic properties (laughing gas).
Nitrogen dioxide (in Insane_Man’s link) is not the gas produced by the body from l-arginine, that’s nitric oxide.
From the American Meteorological Society glossary