The role of fixed nitrogen in atmospheric photochemistry

Among the N compounds released to the atmosphere, ammonia as well as nitrous oxide, nitric oxide, and nitrogen dioxide are most important. Various microbial and human activities constitute the main sources of these compounds. Ammonia strongly influences precipitation chemistry, but its role in atmospheric photochemistry is probably not very important. The oxides of nitrogen, however, must be regarded as key compounds. Nitrous oxide seems to be inert in the troposphere, but its oxidation is the main source of NO in the stratosphere. The more reactive nitric oxide and nitrogen dioxide act as catalysts in various photochemical reaction chains which affect the residence times of many carbon, sulphur, and halogen compounds in the atmosphere through the role that they play in the ozone balance of the atmosphere. The atmospheric abundance of nitrous oxide, nitric oxide, and nitrogen dioxide and a variety of halogen compounds is increasingly influenced by man. As one of the consequences, one m ay expect changes in the abundance of atmospheric ozone, perhaps leading to increased intensity of ultraviolet radiation at ground level or climatic changes.