Oxides of Sulphur :- as Pollutant

The two oxides of sulphur, I.e. SO2 and SO3 are the most serious pollutants of the atmosphere. Both are colourless gases with pungent smell.

Natural Source of release of sulphur dioxide into the atmosphere is the volcanic eruptions. It accounts for about 67% of the total amounts of sulphur dioxide present on the globe. The remaining 33% is discharge into the atmosphere due to human activity.

Man-Made Sources mainly include the following :-
* Combustion of sulphur containing coal and fuel oil in the thermal power plants.
* Roasting of sulphide ores in the smelting industries.
* A small amounts of sulphur dioxide undergoes photolytic oxidation in the air to form SO3.
* In the presence of water vapours, SO3 reacts to form sulphuric acid. Which remains suspended in the air as droplets or comes down in the form of acid rain.

Harmful Effects of Oxides of Sulphur :-
* SO2 and SO3 are both strongly irritating to the respiratory tract. SO2 at concentration of 5 ppm cause throat and eye irritating. It causes breathlessness and affects larynx, I.e voice box. SO3 is more harmful even at a concentration of 1 ppm and causes severe discomfort. Elderly persons and those with heart and lung disease are most seriously affected.
* Even a very low concentration of sulphur dioxide has a very damaging effects on the plants. If exposed for a Long time , a few days or weeks , it shows down the formation of chlorophyll resulting in the injury to the leaf including loss of green colour. This is called chlorosis.
* Sulphur oxides as such or after beings converted into sulphuric acid damage a number of material :

(a) They damage building material like especially marble.

(b) They corrodes metals, particularly iron and steel.

(c) They bring about fading and deterioration of fabrics leather and paper.

(d) They affect the colour of the paints.

Control of Oxides of Sulphur pollution :- The sulphur oxides pollution can be controlled in a number of ways as follows :-

* By use of low sulphur or sulphur free fuels like natural gas.

* By removing sulphur from the fuel before burning.

* By making sulphur free liquefied gaseous fuel from coal.

* By using alternate sources of energy , e.g hydroelectric power plants and nuclear plants.

* By removal of Oxides of sulphur from flue gases.