Nitrogen oxides (NOx) are reactive gases that cause a host of environmental concerns impacting adversely on human health and welfare. Nitrogen dioxide (NO2), in particular, is a brownish gas that has been linked with higher susceptibility to respiratory infection, increased airway resistance in asthmatics, and decreased pulmonary function.

Other effects:

• Principle cause of ground-level ozone formation
• Contribute to acid deposition, which can damage trees at high elevations and increases the acidity of lakes and streams, which can severely damage aquatic life
• Contribute to increased levels of particulate matter by changing into nitric acid in the atmosphere and forming particulate nitrate