Nitrogen combines with oxygen in several compounds, three of which are harmful atmospheric contaminants. Nitrous oxide, N2O, a colorless gas, plays a role in the nitrogen cycle but is not an atmospheric pollutant. Nitrogen oxide (NO) is a colorless poisonous gas that reacts with oxygen and ozone to form nitrogen dioxide, NO2, which is a brownish toxic gas, the principal constituent of photochemical smog. Another compound in smog is dinitrogen tetroxide, N2O4. Mixtures of these toxic oxides of nitrogen are collectively called NOx.
Subjects: Public Health and Epidemiology.