As a class of compounds, the oxides of nitrogen are involved in a host of environmental concerns impacting adversely on human health and welfare. Nitrogen dioxide (NO2) has been linked with increased susceptibility to respiratory infection, increased airway resistance in asthmatics, and decreased pulmonary function (“Air Quality Criteria for Oxides of Nitrogen,” 1993 and “Review of National Ambient Air Quality Standards for Nitrogen Dioxide,” 1995). It has been shown that even short term exposures to NO2 have resulted in a wide ranging group of respiratory problems in school children - cough, runny nose and sore throat are among the most common (Mostardi, Ely, Woebkenberg, Richardson, & Jarrett, 1981). Further, in France, in an ingenious experiment, Dr. Orehek has shown that asthmatics are especially sensitive to even one-hour exposures (Orehk, Massair, Gayrard, Grimaud, & Charpin, 1976). A small group of asthmatics were initially exposed to carbachol, a bronchoconstrictor representative of urban pollen, and then to NO2; adverse effects such as increased airway resistance were experienced by some of the individuals at levels as low as 0.1 parts per million for 1 hour.

NOx also is a contributor to acid deposition, which can damage trees at high elevations and increases the acidity of lakes and streams, which can severely damage aquatic life. Finally, NOx emissions can contribute to increased levels of particulate matter by changing into nitric acid in the atmosphere and forming particulate nitrate.