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As you saw on the previous page there are many types of gases that contribute to air pollution. Humans are largely responsible for pollution but some natural sources of pollution differ from the toxic gases we emit into the atmosphere. Natural sources of sulfur dioxide include release from volcanoes, biological decay and forest fires. Natural sources of nitrogen oxides include volcanoes, oceans, biological decay and lightning strikes. No source really produces Ozone gas. It is a secondary photochemical pollutant formed near the ground by chemical reactions taking place in sunlight. About 10 to 15% of low level ozone, however, is transported from the upper atmosphere (called the stratosphere), where it is formed by the action of ultraviolet (UV) radiation on oxygen (the ozone layer). Plants and trees naturally produce Volatile organic compounds (VOCs). Isoprene is a common VOC emitted by vegetation, and some believe it to be a more significant trigger for asthma and other allergic reactions than man-made irritants. |
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