BDPollution

Most of the energy used in the world comes from the combustion of organic compounds, such compounds are fossil fuels. They are finite resources and when we have used up Earth’s reserves no more will be formed. We use fuels as if there is unlimited reserves but they are not. Although they have many advantages but the disadvantages are taking a toll on our ecosystem. These fuels contain sulphur which when reacts with oxygen and water they form acidic rain. However the biggest drawback is the formation of carbon dioxide or greenhouse gas.

Carbon monoxide and hydrocarbons are present in vehicle exhaust gases as a result of the incomplete combustion of fuel in the engine. Oxides of nitrogen are present in the air is at the temperature of the car engine.
The exhaust gases are passed through a catalytic converter a pipe containing a solid catalyst, plantinum and rhodium. The converter cannot remove oxides of nitrogen.
An engine can be fitted with a three-way catalytic system which can both oxidise fuel, carbon monoxide and also reduce oxides of nitrogen.
Lead poisons the catalyts in the converter.It destroys the catalytic action. Hence unleaded petrol must be used when using a catalytic converter.

The simultaneous production of overoxidised pollutants,nitrogen oxide, and underoxidised pollutants, hydrocarbons and carbon monoxide, makes it difficult to clean up the exhaust with a single chemical treatment. The production of each major pollutant depends on the air/fuel ratio. A rich mixture(with less air than the ideal ratio) leads to the formation of carbon monoxide and hydrocarbons. A lean mixture (with excess of air) leads to the formation of nitrogen oxide. Altering the air/fuel ratio merely trades one set of pollutants for another.

Nitrogen oxide:
This oxide is a pollutant which attacks the ozone layer. It also contributes to the photochemical smog (i will explain this later) and to the formation of nitric acid in acid rain.

Carbon monoxide:
This is a poisonous gas. Hydrocarbons by themselves cause little damage, but in the presence of sunlight react with oxygen, ozone and oxides of nitrogen to form photochemical smog. One solution to the problem of pollution by vehicle exhausts is the catalytic converter.

The petrol engine powers most of our motor vehicles. The burning of fuel in the cylinder after ignition by the spark is sudden and intense. The temperature soars about 2800 Celcius and some nitrogen and oxygen in the cylinder combine to form nitrogen oxide. As the piston is pushed of the cylinder, the combustion gases expand and cool in less than a hundredth of a second. The heating-cooling cycle occurs so rapidly that much of the fuel is not completely oxidized to carbon dioxide and water. Some carbon monoxide is formed and some hydrocarbons remains unburned.

To be continued