In common usage, emission is often the giving off of gases from industrial processes of factories and transportation. As they occur on an industrial scale, even relatively harmless gases can have an undesired effect (such as carbon dioxide contributing to the greenhouse effect). See also Emission trading and automobile emissions controlAutomobile emissions control covers all the technologies that are employed to reduce the air pollution-causing emissions produced by automobiles. Emissions control systems began to be employed in the late 1960s in the U. state of California, followed by t.
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