An Introduction to Environmental Awareness

Unit 4 some cities, where on days, when there is not much wind; a brown layer smog (mixture of fog and smoke) hangs in the air. The relatively inefficient combustion of fuel in a car engine cause many hydrocarbon fragments to be left unburned. These fragments (mainly methane and other alkynes) help to form smog and are believed to be carcinogenic. The incomplete combustion o f fuel produces also carbon monoxide (CO). It is poisonous and at moderate concentrations can cause drowsiness and impair mental and physical alertness. Carbon monoxide emissions largely come from cars exhaust. Nitrogen oxides (NOx) are formed within the cylinders of an engine during fuel combustion. They are major components of smog and it is particularly difficult to deal with them in the engine. If more air is introduced into the cylinder to burn the carbon monoxide and hydrocarbons efficiently, the temperature is raised and more nitrogen oxides are formed. 3. Hydrocarbons and nitrogen oxides in vehicle exhausts combine with one another in sunlight to produce ozone. The ground level ozone is a major air pollutant. The photochemical smog is worst in traffic-congested cities on hot, dry summer days, whereas sulphur based smog occurs on cold, damp winter days. Photochemical smog is especially common when the vehicle engines are old and poorly maintained, as often occurs in developing countries. In some overpopulated cities such as Mexico-City and San Paulo almost all children suffer from coughs and wheezing, different forms of allergies. This is mainly due to the effects of ozone and other motor vehicle pollutants. Poor air quality can have a damaging effect on the lungs of children. High level of air pollution increases the risk of retarded lung development determining their breathing capacity and health for the rest of their life. 4. Air in large cities contains a great deal of dust - suspended in air minute solid particles. Some of them are toxic and can contain lead. Lead comes from petr...