Even though air pollution has existed for generations, both the definition of pollution and the classification of a substance as a pollutant are in Transition. The definition of pollution has been evolving at an incredible rate. Although carbon dioxide was not classified among the primary air pollutants in the 1970s, it is now universally recognized that it has a significant impact on ecosystems. Nowadays, not only increased concentration of carbon dioxide is considered a pollutant but there are many other air pollutants like sulfur dioxide, nitrogen oxide, carbon oxides, particulate matter, volatile organic compounds, etc.