In polluted urban areas, they also enhance production of ozone, a key ingredient of smog that is potentially toxic to animal and plant life.
在受污染的市区，他们还促进臭氧的产生，臭氧是对动物和植物生命有潜在毒性的烟雾的关键成分。
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We had already reduced toxic air pollution from chemical plants by 90 percent, and had set tough standards to reduce smog and soot that would prevent millions of cases of childhood asthma.