Nitrogen Oxides

The term NO_xrefers to nitric oxide (NO) and nitrogen dioxide (NO₂). Nitrogen oxides have both natural and anthropogenic sources. The major anthropogenic source of nitric oxide is the high temperature combustion of fuel in automobile engines and power plants. Larger quantities of nitric oxide are released along with much smaller quantities of nitrogen dioxide as a result of a reaction between nitrogen and oxygen. This reaction is caused by the high temperatures. NO and NO₂ also occur naturally in the atmosphere as a result of bacterial action. Concentrations in urban areas range from between 10 -100 times the concentrations in non urban areas. High concentrations of nitrogen oxides can result in respiratory problems, lowering the body's resistance to infections, as well as participate in the production of photochemical smog (Ahrens, 1991).

The graphic at the right (click on the graphic to see full-sized) shows sources of NOx for the United States.

Graphic from US EPA

The graphic at the left (click on graphic to see full-sized) shows NOx emissions in the United States by county. On this chart, the legend indicates that red color represents the highest levels of NOx emissions. It should come as little surprise that the highest concentrations are in the heavily-populated areas, such as eastern United States and the coast of California.