OXIDES OF NITROGEN IN THE EARTHS ATMOSPHERE - TRENDS, SOURCES, SINKS AND ENVIRONMENTAL IMPACTS

The oxides NO and NO2 of nitrogen (collectively known as NO(x)) play important roles in atmospheric chemistry. They are emitted to the atmosphere naturally, mainly as a result of microbial activities in soils and lightning discharges. However, predominantly, the emissions occur as a result of human activities (such as the combustion of fossil fuels, biomass burning and the use of fertilisers). Long-term trends of the concentration of NO(x) in the atmosphere are not documented adequately. Nevertheless, reconstructed emission inventories suggest that large increases have occurred throughout this century. Exposures to NO(x) compounds have direct adverse effects on humans, animals and plants. NO(x) also contribute to the global environmental problems facing our planet (i.e. excessive global warming, depletion of the ozone layer and acid deposition). In this study, up-to-date knowledge concerning (i) the atmospheric concentration, (ii) sources, (iii) sinks, and (iv) environmental impacts of NO(x) are reviewed.