The researchers noted that proving that air pollution from vehicles caused illness was difficult.

研究人员指出，要证明车辆导致的空气污染会造成疾病并不是一件容易的事，因为这些被研究的污染物既来自汽车、卡车，也来自其他工业。

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Exhaust gases from boilers, vehicles, etc., cause air pollution in cities.

锅炉和车辆等排出的废气，污染城市空气。

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With the growing increase of the retention of the vehicles in the city, the gas emitted from vehicles has become the most important source of the urban air pollution.

随着城市机动车保有量的不断增长，机动车尾气污染问题已经成为城市空气污染最重要的来源，控制机动车尾气污染也已经成为改善城市大气环境质量的当务之急。

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The Commission will need to ensure that the move towards diesel vehicles to improve efficiency does not lead to increased local air pollution from particulates.

BBC: Car drivers 'will save cash thanks to CO2 rules'

Professor Roy Harrison, a member of two UK government advisory committees on air pollution, said US research had provided strong evidence that fine particles contained in emissions from vehicles and industry caused cancer.

BBC: Traffic

In 2002, the state assembly passed a law regulating emissions of CO2 from vehicles, based on a provision of the Clean Air Act that allows California to adopt stricter pollution standards than the federal government (other states can then choose to follow the Californian standards if they wish).

ECONOMIST: The Supreme Court breathes down the government's neck