ACID RAIN 

The atmosphere is a dynamic system, which absorbs various pollutants and thus acts as a 'natural sink'. The atmosphere is filled with virtually everything that is light enough to be carried by the wind. Waste products from the industries, burning of coal, natural gas — the fossil fuels are a main source of pollutants. 

When gases like sulphur dioxide and oxides of nitrogen mix with water vapour in air and form sulphuric acid and nitric acid, respectively. When clouds of acidic water containing sulphuric acid and nitric acid precipitate, acid rain takes place.

FACT: It is suspected that the marble of Taj Mahal is slowly being damaged by acid rain.

Picture credits: Google