Oxides of Nitrogen: Environmental effects
Description
Excessive levels of the oxides of nitrogen, particularly nitrogen dioxide (NO2), can cause death in plants and roots and damage the leaves of many agricultural crops. NO2 is the damaging component of photochemical smog. Excessive levels increase the acidity of rain (lower the pH), and thus lower the pH of surface and ground waters and soil. The lowered pH can have harmful effects, possibly even death, on a variety of biological systems.
Entering the environment
Oxides of nitrogen are part of the biogeochemical cycling of nitrogen, and are found in air, soil and water.
In the atmosphere, the oxides of nitrogen are rapidly equilibrated to nitrogen dioxide (NO2), which eventually forms acid rain. In the stratosphere, oxides of nitrogen play a crucial role in maintaining the levels of ozone. Ozone is formed through the photochemical reaction between nitrogen dioxide and oxygen.
Where it ends up
Oxides of nitrogen are rapidly broken down by reacting with other substances found in the air. Nitrogen dioxide can form nitric acid in sunlight, and is a major constituent of acid rain, tropospheric ozone and smog. Nitrogen oxides react in the soil and the water to nitric acid.
Environmental guidelines
The following ambient air quality standards were established for nitrogen dioxide in 1999:
Averaging period of 1 hour, a maximum of 0.12 parts per million, with a maximum allowable exceedence of 1 day per year.
Averaging period of 1 year, a maximum of 0.03 parts per million.
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