How is `SO_(2)` an air pollutant ?

Explanation

`SO_(2)` acts as an air pollutant because of the following reasons : (i) `SO_(2)` is strongly irritating to the respiratory tract. `SO_(2)` at a concentration of 5 ppm causes throat and eye irritation (resulting in cough, tears and redness in eyes). It causes breathlessness and affects larynx, i.e., voice box.
(ii) Even at a low concentration of 0.03 ppm, it has a very damaging effect on the plants. If exposed for a long time, i.e., a few days or weeks, it slows down the formation of chlorophyll resulting in injury to the leaves including loss of green colour. This is called chlorosis.
(iii) `SO_(2)` dissolves in rain water and produces acid rain which damages bulding materials especially marble `(CaCO_(3))`. ltbgt `CaCO_(3) + H_(2)SO_(3) rarr CaSO_(3) + H_(2)O + CO_(2)`
It corrodes metals particularly iron and steel. It also brings about fading and deterioration of fabrics, leather, paper, etc. and affecting the colour of paints.