AIR POLLUTION

Air pollution is the introduction of particulates, biological molecules, or other harmful materials into Earth's atmosphere, causing diseases, death to humans, damage to other living organisms such as animals and food crops, or the natural or built environment.
    SOURCE: Wikipedia 

CLEAN AIR...

is made up of nitrogen, oxygen and argon, with traces of other gases such as carbon dioxide. Air pollutants mainly come from the discharges of gases and particles, mostly from industry motor, vehicles and domestic wood burning. There are also natural sources such as windblown dust and smoke from bush-fires. Some forms of air pollution create global problems requiring international solutions; for example, upper-atmosphere ozone depletion and acid rain. The enhanced greenhouse effect also falls into this category.

SOURCE:  EPA Victoria