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》
2
Nitrogen dioxide is a pollutant emitted by automobiles.
二氧化氮是汽车排放的一种污染物。
3
Sulfur dioxide, a major contributor to acid rain, is an especially serious pollutant because it diminishes the respiratory system's ability to deal with all other pollutants.