Nitrogen Oxides

Trends in primary pollutants in the
southern Appalachians from 1940-1995

Nitrogen oxide can affect visibility, acid deposition, and ground-level ozone. The primary form of nitrogen oxide emissions is nitric oxide. This gas is rapidly converted in the atmosphere, in the presence of volatile organic compounds and sunlight, to nitrogen dioxide which can subsequently be decomposed by sunlight to produce ozone. Nitrogen oxides are a controlling factor in the formation of ground-level ozone in rural areas of the southeastern United States (Chameides and Cowling 1995). Nitrogen dioxide, when trapped in sufficient quantities, can affect visibility by creating a brownish haze. Secondary pollutants formed from nitrogen oxides also contribute to acid deposition (SAMAB 1996)

The two largest emission sources of oxides of nitrogen are motor vehicles and electricity-generating plants that burn fossil fuels. These two sources have approximately equal annual emissions. Nationally, emissions of nitrogen oxides in the United States rose between 1940 and 1994 (see figure at right). Part of the increase in the southern Appalachians is attributable to a rise in the number of vehicle miles driven and in part to increases in electricity generation. Emissions of nitrogen oxides in the southern Appalachians are projected to increase by 2010 as vehicle miles increase and as electrical power demand rises with an increasing population (SAMAB 1996).