A brown haze indicates a combination of dust, nitrogen dioxide, and nitric oxide from car exhaust, power plants and factories.
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Barry Lefer/MILAGRO

Releasing Nitrogen Pollutants to the Air

While most of the air in our atmosphere is made of nitrogen gas, there are other gases in our atmosphere that contain nitrogen too. 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.

Molecules with one nitrogen atom and one or two oxygen atoms are called nitrogen oxides. They are made in the engines of cars, in power plants, and in factories. These little molecules can cause smog if they combine with oxygen and the fumes from paint and gasoline. They can also cause acid rain if they mix with water vapor in the air. Sometimes they break apart in sunlight and the oxygen atoms latch onto oxygen molecules forming dangerous ground-level ozone.

Molecules with two nitrogen atoms and one oxygen atom are a greenhouse gas called nitrous oxide. The amount of nitrous oxide in the atmosphere has increased in the past 150 years. More greenhouse gases in the air cause global warming. Nitrous oxide forms in car engines, power plants and factories. It also comes from farm animals, sewage, and fertilizer. There are natural ways that nitrous oxide gets into the atmosphere too, including from tiny microbes in the soils of tropical forests.

Last modified May 9, 2007 by Lisa Gardiner.

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