Nitrogen Oxides (NOx)
Nitrogen is an essential element to all living organisms that helps to produce proteins and other vital cell chemicals necessary for life. Constituting 78% by volume of the earth’s atmosphere and recognized as the main element in air, Nitrogen is a colorless, nontoxic, nonflammable, and odorless gas. The stable Nitrogen molecule consists of two atoms of Nitrogen (N2). Nitrogen is known to be an inert (unreactive) gas that is used in electrical systems, chemical/food packaging, and in drying and preparation of refrigeration systems. Even though Nitrogen is imperative for life, Nitrogen gas can mix with other chemicals and sunlight to form pollutants.
When Nitrogen combines with oxygen in air at high temperatures, several different gaseous compounds are produced called Nitrogen Oxides. Although Nitrogen Oxides are emitted by fossil fuel combustion, engraving, dynamite blasting and exhaust from automobiles, Nitrogen Oxides mainly occur naturally by lightning, volcanic, and bacterial action. Nitrogen Oxides can also be produced commercially by reacting Nitric acid with metals or cellulose.
The two main compounds of Nitrogen Oxides are Nitric Oxide (NO) and Nitrogen Dioxide (NO2). These compounds contribute a major role in the atmospheric reactions that produce acid rain and Ozone (O3). Nitric Oxide is a toxic, colorless, flammable gas with a sharp, sweet odor. Nitrogen Dioxide is a reddish-brown, nonflammable gas with a strong, harsh odor. It is highly toxic and a strong oxidizing agent that reacts with sunlight in air to form corrosive Nitric acid.
With the presence of Nitrogen Dioxide, Nitrogen Oxides poses harmful health and environmental effects. Specifically, acute exposure may cause irritation to the lungs and measurable decrease in lung function. Chronic exposure may destroy lung tissue, causing emphysema. Nitrogen Oxides can also destroy vegetation by bleaching or killing plant tissue. In addition, nitrogen oxides may cause metals to corrode due to the formation of Nitrate salts.
Although Nitrogen Oxides are noted for being pollutants, they are used in the production of lacquers, rocket fuels, explosives, and nitration of organic chemicals. Straight activated carbon has a limited capacity for Nitrogen Oxides. The use of an appropriate specially impregnated carbon is recommended.