Pollutant

There are a variety of definitions of the term "pollutants". The most widely accepted definition of "pollutants" is that the man-made materials which can damage or badly affect the eco-system.

Traditionally, carbon dioxide is NOT a pollutant (as in present CE and AL syllabi) because carbon dioxide is a neutrally-exist gas and a major part of carbon dioxide comes from natural processes such as respiration of living organisms. Nowadays, there is a tendency to include carbon dioxide as a pollutant because the Global Warming caused by carbon dioxide is a serious problem to human beings.

2010-02-25 23:41:36 補充：
In the 2nd paragraph, "because carbon dioxide is a neutrally-exist gas and ....." should read "because carbon dioxide is a naturally-exist gas and ......".

Pollutants means something which are pollut some places.

Carbon dioxide is a kind of pollutant, it is because carbon dioxide warms the earth, cause global warming.