Oxides of sulphur:

         It includes SO₂, SO₃. It is a colorless gas having sharp, pungent and suffocating odour. It is soluble in water and forms H₂SO₄.

Source:

(i)     Natural sources such volcanic eruptions.

(ii)   Burning of fossil fuels in thermal power plants, electric power plants.

(iii) Transportation.

(iv) Petroleum refining and cement manufacturing plant.

Sink:  in the atmosphere SO2 is converted to SO3 photo chemically and catalytic and catalytic processes using ozone.

                                 SO₂ + O₃            SO₃ +O₂

SO₃ combine with water vapour to produce H₂SO₄ which give rise to the so called "acid rain" droplets.

                                 SO₃ + H₂O          H₂SO₄

H₂SO₄ combine with lime mineral and forms sulphate thus removed from atmosphere.

Effects:

(i)     It irritates the respiratory tract, eye and causes throat problems.

(ii)   It has got damaging effects on building, marble and lime stone.

(iii) It damages agriculture and slow down formation of chlorophyll resulting in loss of green color of leaf.

         Control of SO2: SO2 can be removed by number of ways.

(i)     Use of fuels having low content of sulphur.

(ii)   SO2 can be removed from exhaust gases by use of chemical scrubbers, such as lime stone and citric acid.