In western countries, "second-hand fragrance" has been deemed a source of air pollution for a long time.

在西方一些国家，“二手香”早就被视为空气污染源之一。

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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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According to a report issued in 2005 by the European Union, "ships are fast becoming the biggest source of air pollution in the EU."

欧盟在2005年发表的一份报告指出，“船只正在快速成为欧盟最大的空气污染来源。”

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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).

FORBES: Acceleration of the Natural Gas Highway

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.

CNN: Smog-eating tiles gobble up air pollution