CHEMISTRY - Troposphere Pollution

The five major pollutants present in the air :-

1. Carbon monoxide
2. Hydrocarbon
3. Oxides of nitrogen
4. Oxides of sulphur
5. Particulates

Now, we shall discuss the sources, harmful effect and the method to control each of these pollutant. It is colourless, odourless and tasteless gas. It is 96.5% as heavy as air.

* Sources of Carbon monoxide production :-

(a) Due to human activity :-   

*  Incomplete combustion of fossil fuels or hydrocarbon fuels in the automobiles.
* Forest fires or agricultural wastes burning.
* Reaction of carbon dioxide with carbon containing material at high temperature.

(b) Natural sources :-
* From conversion of methane produced by the bacterial decay ogre living or organic matter (80%).
* From synthesis and decay of chlorophyll (3%).
* From oceans and other undetermined sources (10%).

Harmful Effect of Carbon monoxide :- carbon monoxide is poisonous because it combines with hemoglobin of the red blood corpuscles about a 200 times more easily than does oxygen to form carboxyhemoglobin reversibly as follows :-
                Hb. + CO - HbCO
The normal function of the hemoglobin is to combines with Oxygen in the lungs to form hemoglobin.
The oxyhemoglobin travels to the different body cells where it gives up oxygen and takes up carbon dioxide for returns to the lungs which is then exhaled out. However, if large amounts of carbon monoxide is present in the surrounding air, it combines more readily with the hemoglobin. Thus, transport of oxygen to the differents parts of the body is inhibited. In other words, the body becomes oxygen-starved.

Control of Carbon monoxide pollution :- The main source of CO pollution due to human activities is the use of internal combustion engine in the automobiles. These engine emit a mixture of CO , Oxides of nitrogen and particulates. However, any method used to control any one of these pollutants result in the increase in the other pollutants. A few method of controlling a CO Pollution are as follows :-
* The carbarettor is adjusted so as to give a proper air fuel ratio.
* The exhaust system is developed in such a way that it brings about complete combustion in the fuel so that negligible CO is formed.
* Catalytic converters can be fitted into the exhaust pipe which may convert the poisonous gases like CO into harmless products before they are thrown into the air.
* Modifications of internal combustion engine have been done by certain companies like Honda and Toyota of Japan instead of catalytic converters.
* Instead of gasoline , the use of CNG ( Condensed Natural gas ) and LNG ( Liquefied natural gas ) has been started as they are pollution free fuels.

2. Hydrocarbons as pollutants :- Many differents hydrocarbons are present in the air. Most of these hydrocarbons are of low molecular mass and are gases or volatile liquids at ordinary temperature. Methane the simplest hydrocarbons is the most abundant hydrocarbon carbon pollutant. In Los Angeles ( in USA ) where the vehicular traffics is very high , its amounts in the air was found to be 3ppm in 1965.

Sources of Hydrocarbons :-
(a) Natural Sources :-
* Trees emit large amounts of hydrocarbons in the air.
* Methane is released into the air in large quantities by the anaerobic decomposition of organic matter in soil, water and sediments.
* Domestic animals contributed a very huge amount of methane into the air every years.

(b) Man-Made sources :-
* Just as in case of CO , the largest man-made source of hydrocarbons pollutant is the internal combustion engine. About a 15% of the total hydrocarbons present in the air is from this source.
* Some hydrocarbon pollution also takes places due to burning of stationary fuel , I.e coal , wood, kerosene oil etc.
* Evaporation or organic solvent like benzene, toluene etc. during industrial operations add sub- stantially to the total hydrocarbon pollution.

Harmful Effects of Hydrocarbon Pollution :-
* At low concentrations, as they exist in through air at present, there are no harmful effects of the hydrocarbon on human beings. However , if their concentration rises to 500-1000 ppm, they have carcinogenic effect on the lungs and cause cancer.
* Due to their photochemical reactions with oxygen and oxides of nitrogen , they form photochemical oxidants and photochemical smog which have a strong damaging effect on the human beings as well as plants.

Control of Hydrocarbon Pollution :- As automobiles are the main sources of hydrocarbon pollution, all those steps taken to control CO pollution are needed for controlling hydrocarbon pollution. 

3. Oxides of Nitrogen .

4. Oxides of Sulphur .

5. Particulates .