United Nations Environment Programme

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Facts on Pollutants:

Ground-level Ozone (O3)

Ozone is a pale blue gas and has a sweetish odour. Ozone is a strong oxidant, thus making it very reactive and capable of combining with many organic compounds in cells and tissues, as well as with rubber and other materials. Ozone is found in the lower atmosphere (ground-level ozone – also a main component of photochemical smog) and higher up in the stratosphere (stratospheric ozone). Whereas ground-level ozone is bad for your health, stratospheric ozone protects us from ultraviolet radiation. Therefore, ground-level ozone should be minimized, and the natural occurrence of stratospheric ozone should be protected.
Sources of Ground-level Ozone:
Ground-level ozone is formed in a complex chain reaction involving sunlight, NOx and HCs. High levels of ground-level ozone are typically found in areas with high traffic densities (such as major cities) and where emissions of NOx and HC are high.


Human Health Effects of Ground-level Ozone:
Ground-level ozone is an irritant to the lungs, eyes, nose, throat, and respiratory tract. Exposure can lead to decreased pulmonary functions (heart and lung functions) in young adults and children. Another effect of ground-level ozone on the lungs is an increased incidence of asthmatic attacks and respiratory symptoms.


Environmental Effects of Ground-level Ozone:
Ground-level ozone causes damage to animals and plants (e.g. interference with plant growth, reproduction and overall health).

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