![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Module 6: Air Pollutants and Control Techniques - Nitrogen Oxides - Characteristics
Lesson Material
Practice Problems
Objective
- Identify the basic characteristics of nitrogen oxides.
Due to cleaner fuels and more efficient engines, total emissions of
nitrogen oxides from mobile sources has decreased over the past twenty
years. However mobile sources, along with electric utilities, continue
to be the leading contributor of nitrogen oxide emissions as shown in
Figure 1.
Nitrogen oxides (often abbreviated NOx) are nitric oxide (NO) and nitrogen dioxide (NO2). They are formed simultaneously in combustion processes and other high temperature operations such as metallurgical furnaces, blast furnaces, plasma furnaces, and kilns. Nitrogen oxides can also be released from nitric acid plants and other types of industrial processes involving the generation and/or use of nitric acid (HNO3).
Nitric oxide is a colorless, odorless gas. It is essentially insoluble in aqueous liquids. Nitrogen dioxide is moderately soluble in aqueous liquids. At low temperatures such as those often present in ambient air, nitrogen dioxide can form a dimer compound (N2O4) that has a distinctly reddish-brown color. This compound contributes to the brown haze that is often associated with photochemical smog incidents. Nitrogen dioxide has a pungent acid odor.
Both nitrogen oxide compounds are toxic; however, the ambient levels of nitrogen oxides are usually well below the concentrations believed to contribute to adverse health effects. The low ambient concentrations are due primarily to the relatively rapid reactions that occur when NO and NO2 are emitted into the atmosphere.
The main reason for regulating nitrogen oxide emissions is the suppression of these atmospheric reactions, which create ozone and other reaction products that are associated with adverse health effects. Nitrogen oxides are one of the most important reactants in ozone formation. In fact, nitrogen dioxide is the main gas phase species responsible for the absorption of light in the photochemical reactions that cause smog formation.
Practice Problems
Nitrogen Oxides - Characteristics
- Instructions:
- Complete the Practice Problems before proceeding to the next section. Click on the button below.