Explain tropospheric pollution in 100 words.

Tropospheric (air pollution) pollution refers to that part  of atmosphere which is nearest to the earth's surface extending to a height of about 80 km. It includes:
(i) Gases such as oxides of sulphur, CO, oxides of nitrogen and hydrocarbons.
(ii) Particulate matter such as dust, smoke, fumes etc. 
(iii) Radioactive materials and many others.
It should be noted that these substances are naturally present in the atmosphere in low concentration, but they become pollutants when their concentration is relatively high.
Most of these pollutants can cause damage to human health and some pollutants (such as SO₂) can produce a corrosive effect on building materials.