Acid Rain:- It is a secondary pollutant. It is formed due to action of 1^o pollutant with environmental failure. Automobile exhaust and burning of fossil fuel mainly responsible for acid rain. It causes chlorosis and also causes mortality in aquatic organism.

Acid rain decrease the shining of marble and causes corrosion in marble.

Acid rain can be formed even in dry dust. 1^st rainfall of any season’s acid rain, refinery of Mathura causes greater threat to Taj Mahal of Agra.

SO₃ + H₂O  => H₂SO₄  

NO₂ + H₂O  => HNO₃