Nitrogen oxides are present all around us, as a mostly unfortunate byproduct of industrial civilization. While they have many beneficial uses, they can also be heavy pollutants.
Nitrogen oxides are gases made up of nitrogen and oxygen. Many of them can be man-made and extremely harmful to human health. The most common ones are nitric oxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O).
Most of them are colorless or brownish at room temperatures, and have a distinctive smell.
Nitric oxide is used to bleach rayon and produce nitric acid. Nitrogen dioxide is used to produce among other chemicals rocket fuels and explosives. Nitrogen dioxide is sometimes used to bleach flour.
Nitrogen oxides are polluting the air through car exhaust, electric power plants, the burning of various fuels, cigarette smoking, electroplating, welding etc.
When combined with volatile organic compounds, nitrogen oxides form smog; when combined with sulfur dioxides, they form acid rain.
Depending on the level and length of exposure, nitrogen oxides can cause serious health problems: