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.