smog
Smog is a type of air pollutant. The word "smog" was made in the early 20th century as a portmanteau of the words smoke and fog to refer to smoky fog. The word was then intended to refer to what was sometimes known as pea soup fog, a familiar and serious problem in London from the 19th century to the mid 20th century. This kind of smog is caused by the burning of large amounts of coal within a city; this smog contains soot particulates from smoke, sulfur dioxide and other components.Modern smog, as found for example in Los Angeles, is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emissions to form photochemical smog. In certain other cities, such as Delhi, smog severity is often aggravated by stubble burning in neighboring agricultural areas. The atmospheric pollution levels of Los Angeles, Beijing, Delhi, Mexico City and other cities are increased by inversion that traps pollution close to the ground. It is usually highly toxic to humans and can cause severe sickness, shortened life or death. 雾霾是一种空气污染物。雾霾一词诞生于二十世纪初期，是雾和霾的合成词，被用于指代烟雾。后来，这个名词有时也用于指浓雾，如十九世纪至二十世纪中期伦敦严重的大气污染问题。这种雾霾是由于在城市内大量焚烧煤炭所产生的，主要成分包含浓烟里的微尘，二氧化硫，和其他成分。
以洛杉矶的光化学烟雾污染为例，现在的雾霾是一种衍生于机动车排放的大气污染，内燃机排放的气体和工业硅粉在紫外线作用下形成二次污染物，而二次污染物与私家排放气体形成光化学烟雾。在一些城市， 如印度的德里，临近农业地区焚烧秸秆所产生的气体恶化了雾霾的严重程度。洛杉矶，北京，德里，墨西哥城和其他一些城市的大气污染程度由于逆温层接近地面而恶化。这种雾霾对人来说剧毒无比，能导致严重疾病，缩短人寿命，甚至是死亡。 :D雾霾太可怕了
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