Uncontrolled it is a serious source of air pollution.

如果不进行控制将造成很严重的环境污染。

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Cars, being the greatest source of air pollution, can be left at home this weekend.

汽车是空气的主要污染源，这个周末可以别开车了。

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At the same time the vehicle exhaust has become the primary source of air pollution in big cities.

同时在我国大城市机动车排气污染已成为城市空气污染的主要源头。

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This will allow truckers to reduce emissions significantly (diesel emissions include nitrous oxides, particulate matter, and other air toxics and they are a major source of pollution in some areas).

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Janice Nolen, national policy adviser at the American Lung Association, says that rather than dealing with the harmful effects of air pollution, the focus should be on tackling the problem at source.

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