词条 | smog |
释义 | smog atmosphere community-wide polluted air. Although the term is derived from the words smoke and fog, it is commonly used to describe the pall of automotive or industrial origin that lies over many cities, and its composition is variable (see video--> ![]() At least two distinct types of smog are recognized, sulfurous smog and photochemical smog. Sulfurous smog results from a high concentration of sulfur oxides in the air and is caused by the use of sulfur-bearing fossil fuels, particularly coal. This type of smog is aggravated by dampness and a high concentration of suspended particulate matter in the air. Photochemical smog, which occurs most prominently in urban areas that have large numbers of automobiles, requires neither smoke nor fog. This type of smog has its origin in the nitrogen oxides and hydrocarbon vapours emitted by automobiles and other sources, which then undergo photochemical reactions in the lower atmosphere. The highly toxic gas ozone arises from the reaction of nitrogen oxides with hydrocarbon vapours in the presence of sunlight, and some nitrogen dioxide is produced from the reaction of nitrogen oxide with sunlight. The resulting smog causes a light brownish coloration of the atmosphere, reduced visibility, plant damage, irritation of the eyes, and respiratory distress. |
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