Question

choose an environmental topic of your choice and write a short 4-5 page essay on that topic.

Paper should include a title and:

I. Introduction to the topic.

2. Key points, including impact on the environment.

3. A conclusion, that includes your view/opinion on the topic.

4. References; include at least one journal/paper/book.

Answer 1

AIR POLLUTION

Pure air is colourless and odourless. But various pollutants from natural and man-made sources are entering the atmosphere daily and these disturb the dynamic equilibrium in the atmosphere. This leads to air pollution when the normal properties of air are upset and both man and environment suffer. Natural sources of air pollution are: • Volcanic activity, vegetation decay, forest fires emitting carbon monoxide, sulphur dioxide and hydrogen sulphide and tiny particles of solids or liquids sprayed from the seas and land by wind. Man-made sources are: • Gases, mists, particulates and aerosols emitted by industries and other chemical and biological processes used by man.

Primary Pollutants :- There are five primary pollutants which together contribute to more than 90 per cent of global air pollution: Carbon monoxide, CO Nitrogen oxides, NOX Hydrocarbons, HC Sulphur oxides, SOX Particulates. Transportation accounts for more than 46 per cent of the total pollutants produced per year and hence remains the principal source of air pollution. Carbon monoxide is the major industrial pollutant, with a tonnage matching that of all other pollutants together. However, particulate pollutants, though minor, are the most dangerous among the primary pollutants

Carbon Monoxide :- CO It is a colourless, odourless and tasteless gas which is injurious to our health. Each year 350 million tonnes of CO are emitted all over the world in which USA alone shares 100 million tonnes. Transportation accounts for 70 per cent of CO emission. Diesel and petroleum engines in automobiles are primarily responsible for about 70 per cent of CO emissions.

The sources of carbon monoxide, CO, are the chemical reactions:

(i) incomplete combustion of fuel or carbon containing compounds:

2C + O2 -----> 2CO

(ii) reaction of carbon dioxide and carbon-containing materials at elevated temperatures in industries, e.g., in blast furnaces: CO2 + C ------> 2CO

(iii) dissociation of carbon dioxide at high temperatures:

CO2 --------> CO + O

Control of CO Pollution The petroleum and diesel-fed automobiles account for major share of carbon monoxide emission. Hence, efforts for carbon monoxide pollution control are mainly aimed at automobiles. Use of catalytic converters in the internal combustion engines of automobiles helps in cleaning up the exhaust emissions. Such converters built into the automobile engines promote oxidation-reduction cycles and ensure complete combustion of carbon monoxide, nitrogen oxides and hydrocarbons. The following figure illustrates the action of catalytic converters: use of catalytic converters in two stages helps in the elimination of pollutants from exhaust gases before they are discharged into the atmosphere.

In the first converter, nitrogen oxides are reduced to nitrogen (+ ammonia) in the presence of finely-divided catalyst platinum, and the reducing gases, carbon monoxide and hydrocarbons. The production of ammonia is kept at a minimum under carefully controlled conditions. In the second converter, air is introduced to provide an oxidizing atmosphere for complete oxidation of carbon monoxide and hydrocarbon into carbon dioxide and water in the presence of finely-divided platinum catalyst.

Nitrogen Oxides :- NOX It consists of mixed oxides, nitric oxide and nitrogen dioxide (NO and NO2, respectively). The former is a colourless and odourless gas but the latter (NO2) has a reddish brown colour and pungent smell.

The formation of NO and NO2 is based on the chemical reactions:

N2 + O2 ----> 2NO

2NO + O2 -----> 2NO2

These reactions occur inside the automobile engines so that the exhaust gases consist of NOX. The latter concentration in rural air is much less than that in urban air. In air NO_X is converted into nitric acid (HNO3) by natural processes: NO2 + O3 -------------> NO3 + O2

NO3 + NO2 -------> N2O5

N2O5 + H2O --------> 2HNO3

This nitric acid is one of the constituents of acid rain discussed in a subsequent section. From auto-exhaust emissions NO_x is removed as discussed above by means of catalytic converters.

Sulphur Dioxide :-  Sulphur dioxide is a colourless gas with a pungent odour. It is produced from the combustion of any sulphur-bearing material. Sulphur dioxide, SO₂, is always associated with a little of sulphur trioxide, SO₃.

S + O2 ------------> SO2

2SO2 + O2 --------> 2SO3

Man-made sources—coal-fired power stations and other industries—contribute about 33 per cent of SO_X pollution while natural sources, viz. volcanoes.

Control of SO_x Pollution SO_x (sulphur oxides) from flue gases of industrial plants can be removed by means of chemical scrubbers. The flue stack gases are led through a bed of (slurry) limestone, CaCO₃ (calcium carbonate) which absorbs sulphur dioxide quite efficiently. The method is economical but the disposal of solid waste, calcium sulphate is a problem. Alternatively, sulphur oxide in aqueous solution is treated with citric acid salt and the resulting solution is exposed to a stream of hydrogen sulphide gas whereby sulphur is deposited. This sulphur can then be recovered and utilised. Thermal power plants, major sources of man-made SO_X pollution, are normally constructed with tall chimneys to disperse the emissions over a wide area. This reduces the local problem but creates problems for far away areas through acid rains.

Acid Rain : - It has been described above that much of nitrogen oxides (NOx) and sulphur oxides (SOx) entering the atmosphere are transformed into nitric acid (HNO3) and sulphuric acid (H2SO4), respectively. These combine with hydrogen chloride (HCl) from HCl emissions (both by man-made and natural sources) and generate acidic precipitation, known as acid rain. Acid rain is a major environmental issue as it badly damages the environment. It damages buildings and structural materials of marble, limestones, slate and mortar. These materials become structurally weak as calcium carbonate reacts with sulphuric acid to form soluble sulphate, which is leached out by rain water. In Greece and Italy, invaluable stones and statues have been partly dissolved by acid rain. Besides these, acid rain damaged forests in Germany and lakes in Sweden and Canada. Acid rain originated from U.K., but far away in Sweden it damaged some 8,000 lakes of which 4,000 are dead. Similarly, acid rain from USA damaged lakes and forests in Canada. In India, the Taj Mahal is threatened by acid rain from Mathura Refinery and other industries.