The Regional Air Pollution Control Agency

Nitrogen oxides

Nature of the Pollutant

There are several oxides of nitrogen, as in the case of sulfur dioxide, but the two most important from an ambient air pollution standpoint are nitric oxide (NO), a colorless gas, and nitrogen dioxide (NO2), a highly toxic, reddish-brown gas. In the atmosphere, NO is usually oxidized slowly to NO2, which may then be converted to other chemical products. Both NO and NO2 are produced by high temperature combustion of fossil fuels, such as the burning of gasoline in automobile engines, or of coal in power plants.

An ambient air quality standard has been established for nitrogen dioxide. There is only a long-term standared (maximum annual arithmetic mean).

The nitrogen oxides cause direct environmental damage by their toxic and irritating effects on plants, animals and humans. They are also indirectly damaging when they combine with moisture to form nitric acid or nitrate salts. Nitric acid contributes to the creation of acid rain, which can have a serious deleterious impact on plant and animal life hundreds of miles downwind of its source. In combination with organic compounds, the nitrogen oxides can also form peroxyacetyl nitrate (PAN), which is an eye irritant and is very toxic to plants. Tiny particles formed by nitrates also are an important component of PM 2.5 (small particulates), a newer criteria pollutant, and very much of concern in the Dayton region.

Nitrogen oxides also are indirectly damaging because they play a major role in the formation of yet another criteria pollutant, ozone.

The monitoring technique

RAPCA has not measured NOx since 1986, at which time it was determined that the NO2 values were so far below the NAAQS that there was little point in maintaining an expensive monitor. At that time we were using the EPA reference method involving the chemiluminescence of NO in reaction with ozone.

More Information

The USEPA is undertaking a review of the nitrogen oxides criteria document (see the EPA review notice ) and note that "All communications and information should be submitted by January 31, 2006."

To view the criteria documents, you might want to go through the site at the U. of Texas School of Public Health