Sulphur dioxide is a pollutant and a major contributor to acid rain.

二氧化硫是一种污染物，并且是形成酸雨的主要因素。

《牛津词典》

Nitrogen dioxide is a pollutant emitted by automobiles.

二氧化氮是汽车排放的一种污染物。

youdao

youdao

In other words, instead of regulating the sediment directly, EPA decided that water was a pollutant.

FORBES: The EPA's Lisa Jackson: The Worst Head of the Worst Regulatory Agency, Ever

The first question facing the justices is whether carbon dioxide is a pollutant at all.

NPR: Supreme Court Hears Global Warming Arguments

Jackson laid the groundwork for administrative action when she declared carbon dioxide a pollutant in 2009.

FORBES: Bill Gates Still Believes In A Carbon Tax