A brown haze indicates a combination of dust, nitrogen dioxide, and nitric oxide from car exhaust, power plants and factories. Click on image for full size (174 Kb) Barry Lefer/MILAGRO

While most of the air in our atmosphere is made of nitrogen gas (two atoms of nitrogen bonded together), there are other gases in our atmosphere that contain nitrogen as well. They may make up only a small percentage of the air molecules in our atmosphere, but their numbers are growing and, even in small amounts, they can cause huge changes in our planet.

Nitric oxide (NO) and nitrogen dioxide (NO2)
Nitrogen dioxide and nitric oxide molecules form during combustion in car engines, power plants, and factories. They can contribute to smog when combined with oxygen molecules and the fumes from paint and gasoline (called Volatile Organic Compounds). They can also contribute to acid rain if mixed with water vapor turning into nitric acid. Nitrogen dioxide will break apart in sunlight and the free oxygen atoms latch onto oxygen molecules forming dangerous ground-level ozone.

Nitrous oxide (N2O)
Also known as “laughing gas,” nitrous oxide is a greenhouse gas. The amount of nitrous oxide in the atmosphere has increased since the beginning of the Industrial Revolution.

Nitrous oxide forms during combustion and is also released into the atmosphere from farm animals, sewage, and fertilizers. There are natural ways that nitrous oxide gets into the atmosphere too, including from tiny microbes that chemically alter nitrogen in the soils of tropical forests.