Since a chief source of pollutants is automobile emissions, it might be expected that pollutant levels could be correlated with automobile traffic, at least to some extent.

因为污染物的主要来源是汽车的排出物，所以可以料想污染物的浓度至少在某种程度上是与汽车运输有关。

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The gauges are used to monitor water and pollutant levels.

WSJ: Susquehanna River commission wants gauge funding

The researchers Katherine Ensor and Loren Raun cross referenced the time and place of the cases against air pollutant levels recorded by the extensive network of air monitors throughout the Houston area.

FORBES: Researchers Prove Air Pollution Causes Heart Attacks

Two Surrey councils have said they will be working together to improve air quality as readings showed levels of a pollutant above government targets.

BBC: Air pollutants in Woking above government target levels