Nitrogen oxides form when fuel is burned at high temperatures, as in a combustion process. The primary sources of NOx are motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels

Where does it come from?
NOx form when fuel is burned at high temperatures, as in a combustion process. The primary sources of NOx are motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels. Utilities: 27% Motor Vehicle: 49% Industrial/Commercial/Residential: 19% All Other Sources: 5%

NOx is one of the main ingredients involved in the formation of ground-level ozone, which can trigger serious respiratory problems. NOx:
• reacts to form nitrate particles, acid aerosols, as well as NO2, which also cause respiratory problems.
• contributes to formation of acid rain.
• contributes to nutrient overload that deteriorates water quality.
• contributes to atmospheric particles, that cause visibility impairment most noticeable in national parks.
• reacts to form toxic chemicals.
• contributes to global warming.

NOx and the pollutants formed from NOx can be transported over long distances,
following the pattern of prevailing winds in the U.S. This means that problems associated with NOx are not confined to areas where NOx is emitted. Therefore, controlling NOx is often most effective if done from a regional perspective, rather than focusing on sources in one local area.

NOx Emissions Are Increasing.
Since 1970, EPA has tracked emissions of the six principal air pollutants - carbon monoxide, lead, nitrogen oxides, particulate matter, sulfur dioxide, and volatile organic compounds. Emissions of all of these pollutants have decreased significantly except for NOx, which has increased approximately 10 percent over this period.

Health and Environmental Impacts of NOx
NOx causes a wide variety of health and environmental impacts because of various compounds and derivatives in the family of nitrogen oxides, including nitrogen dioxide, nitric acid, nitrous oxide, nitrates, and nitric oxide.

If you like to know more about NOx, please check these other web pages

EPA web site
http://www.epa.gov/ebtpages/airairponitrogenoxidesnox.html

South Coast AQMD web site
http://www.aqmd.gov

Texas Commission on Environmental Quality web site
http://www.tceq.state.tx.us/index.html

How does Ozone form?
This link has an excellent animation on how NOx forms Ozone.
http://www.clair.org/HowdoNOx.htm

Glossary of Terms

fuel NOx - results from the combustion of fuels that contain organic nitrogen; this depends on local combustion conditions and nitrogen content of the fuel.

emission standards - used to regulate emissions from industrial sources and to estimate the maximum rate of emissions from a proposed new source.

criteria air pollutants - primary (emitted directly) and secondary (formed by chemical reactions among primary pollutants in the atmosphere) pollutants that pose health-based risks. These include: PM-10 (particulate matter with a diameter less than 10 micrometers), SO2, NO2, CO, particulate Pb, and ozone.

global climate change (GCC) - also termed the "green house effect", refers to the retention of infrared radiation (heat) by certain gases in the atmosphere before the heat is lost to space resulting in enhanced warming of the earth's average global temperature.

point source - emissions from a stationary source.