What is Air Pollution
Pure air is colourless and odourless. But various pollutants from natural and man- made sources are entering the atmosphere daily and they disturb the dynamic equilibrium in the atmosphere. The activity of living organisms and different gases in the atmosphere are found in a definite ratio and proportions. There is a cycling of the gases between the living organisms and environment. It is due to organisms that oxygen and carbon dioxide are found in the balanced level in the atmosphere. Carbon dioxide constantly released into the atmosphere by the respiration of living organisms and oxygen is constantly taken up from atmosphere by the living. organisms for respiration. Green plant absorb carbon dioxide for photosynthesis and release oxygen as a byproduct of photosynthesis due to this process the carbon dioxide and oxygen are maintained in the atmosphere.
The atmosphere is an envelope of gases is divided in to the following layers.
1- Troposphere- This layer is up to five kilometers. The lowest atmosphere in which temperature decreases with height bounded by sea surface. In this layer mainly nitrogen, oxygen, carbon dioxide and water vapors are present.
2- Stratosphere- This layer is from 5 to 45 kilometers. This layer is above the troposphere. The temperature increase up to 90 degree centigrade. Most common chemical compound of this layer is ozone.
3- Mesosphere- This layer is from 45 to 80 kilometers. This layer is between the stratosphere and thermosphere. Most common chemical compound of this layer is oxygen and nitric oxide.
4- Thermosphere- This layer is present above the 80 kilometer. This layer is also called the ionosphere. Chemical compound oxygen and nitric acid is also present in this layer.
Sources
Air pollution is mainly from industry, thermal power station, automobile and domestic combustion etc. There are a number of industries which are the source of air pollution. Petroleum refineries are the major source of gaseous pollutants. Some air pollutants and their sources are given in table 9.1.
The chief gases are sulphur dioxide and nitrous oxide. The major source of sulphur dioxide is the burning of fossil fuels, mostly coal in power plants. Another major source comprises a variety of industrial process, ranging from petroleum refining to the production of cement, aluminum and paper. It is colourless and odourless gas, normally present at the earth surface at low concentration. Higher concentration of sulphur dioxide may cause death of the cells.
Oxides of nitrogen are emitted in several forms like nitric oxide, nitrous oxide and nitrogen dioxide. In unpolluted atmosphere, there are present measurable amounts of nitrous oxide, nitric oxide and nitrogen dioxide. Of these nitric oxide is the pivot compound. It is produced by the combustion of oxygen and nitrogen during lightning discharges and by bacterial oxidation of ammonia in soil. In urban areas about 46% of oxides of nitrogen in air come from vehicles and 25% from electric generation and rest from other sources. In metropolitan cities, vehicular exhaust is the most important source of nitrogen oxide. In atmosphere maximum nitrous oxide levels are about 0.5 ppm, whereas average global levels estimated to be nearly 0.25 ppm. This gas has so far not been implicated in air pollution. At high temperature, combustion of gasoline produces nitric oxide. A large amount of nitric oxide is readily converted to more toxic nitrogen dioxide in the atmosphere. Nitric oxide is responsible for several photochemical reactions in the atmosphere.
Carbon monoxide is highly dangerous gas form when fuels have too little oxygen to burn completely. It spews out in car exhausts and it can also build up to dangerous levels inside your home if you have a poorly maintained stove or fuel burning appliance. Carbon dioxide gas is central to everyday life and it is not normally considered pollutants.
Ozone is formed in the atmosphere through chemical reactions involving certain pollutants on absorption of UV-radiations. The atmospheric ozone is now being regarded as potential danger to human health and crop growth.
Fluorides in atmosphere come from industrial processes of phosphate fertilizers, ceramics, aluminium, fluorinated hydrocarbons, fluorinated plastic, uranium and other metals.
Chloroflurocarbons are one of the harmful gases which are widely used in refrigerators and aerosol cans.
The main source of hydrocarbons is motor vehicles, being emitted by evaporation of gasoline through carburetors, crankcase etc. In India, two and three-wheelers are the main contributors.
In air, the common metal is mercury which is mainly released from industries and human activities in the atmosphere. Mercury compound is mostly used in the production of fungicides, paints, cosmetics, paper pulp etc.
Quality Parameters
Each pollutant in the air has limiting concentration. Air quality measurement is complicated by the lack of knowledge as to what is clean air and by the difficulty in defining quality. Pure air contains only the naturally occurring gases but pure air does not occur in nature. Pollen particle, dust, fog etc. are all natural contaminants. Each pollutant, present in air, has a threshold limit value (TLV) which, if exceeded, causes public health hazards. The list of typical pollutants with their threshold limits are given in table For factory workers TLV set the limit of exposure for 40 hours a week (8 hours a day) without adverse effect. These TLV values are determined mainly by experiments on animals.
Effects
Air pollution can harm the health of people and animals, damage crops or stop them growing properly, and make our world unpleasant and unattractive in a variety of other ways.
1. Green house effect
The sun light that reaches the Earth warms atmosphere and the earth surface. The Earth's atmospheric system then reradiates the heat as infrared radiation. Water vapors and other several gases, including carbon di-oxide, methane and CFCs, warm the Earth's atmosphere because they absorb and reemit radiation. This is called green house effect because it is like the glass of a greenhouse that allows sunlight to pass through and then traps the resulting heat inside the structure. Carbon dioxide is the principal "green house gas" responsible for warming the earth. Carbon dioxide is rising into the atmosphere slowly as a result of large scale burning of fossil fuels. This rise in temperature would result in melting of the polar ice caps and would add more water to the sea. There would be coastal flooding and the possible loss of many cities like Bombay, Calcutta and Trivandrum etc.
2. Ozone shield holes effect
In stratosphere there is a layer of ozone called an ozone shield that absorbs the ultraviolet rays of the sun. Ultraviolet radiation cause mutations that can develop skin cancer and causes eye cataracts. Ultraviolet rays also affect our immune system and also kill off microscopic organisms. Depletion of the ozone layer in recent years is of serious concern. There was a severe depletion of some 40-50% above the Antarctic region every spring. Severe depletion of ozone layer is commonly called "ozone holes". A United Nations Environment Programmed report predicts a 26% rise in cataracts and nonmelanoma skin cancers for every 10% drop in the ozone level.
The cause of ozone depletion is the breakdown of chloro-fluorocarbons (CFCs). The best known CFC is "Freon", a heat transfer agent found in refrigerator and air conditioners.
3. Acid Rains
The oxides of sulphur and nitrogen are important gaseous pollutants in air. These oxides are swept up into the atmosphere and can travel thousands of kilometers. The longer they stay in the atmosphere, the more likely they are to be oxidized into acids. Sulphuric acid and nitric acid are the two main acids, which then dissolve in the water in the atmosphere and fall to ground as acid rain. Acid rain increase the soil acidity, thus affecting land flora and fauna, cause acidification of lakes and streams thus affecting aquatic life, affects crop productivity and human health. Acid rain leaches metals such as lead, mercury and calcium, from the soil and rocks and discharges them into river and lakes.
4. Effect on Tajmahal
The historical monument is losing its lusture day by day due to ill effects of air pollutants. Sulphur dioxide and sulphur trioxide react with water vapour and oxygen to form sulphuric acid and sulphurous acid that act on Taj's marble. As a result, there is a continuous deterioration of this classical building. Marbel of Tajmahal has to be guarded against pollutants by protective coating which could resist the action of air pollutants.
5. Bhopal gas tragedy
The mid night of 2&3 december 1984, Bhopal gas tragedy is a case of air pollution in which Methyl isocynate (MIC) gas released from a fertilizer manufacturing plant of Union carbide caused death approximately 2500 persons. This gas causes irritation which may be followed by blindness and various lung diseases causing death.
6. Agricultural effects
Farming is as much of an art as a science. One of the things that characterized the 20th century was the huge growth in industrial agriculture using fertilizers, Pesticides and so on to increase crop yields and feed the world's ever-growing population.
7. Smog
Smog is harmful to health. It reduces the respiratory system's ability to fight infection and remove foreign particles.
Control measures
Now we know that what is pollution, but what is solution? Steps are to be taken to control pollution at source (prevention) as well as after the release of pollutants in the atmosphere. There is an urgent need to prevent the emission from the above said major source of air pollution. The control of emission can be released in number of ways.
1- Making electricity in conventional power plants generates pollution, so anything can do save energy will help to reduce pollution.
2- Producing cool, clean water needs huge amounts of energy so cutting water waste is another good way to save energy and pollution.
3- Cars are the biggest source of air pollution in most urban areas. So traveling some other way through a town or city helps to keep the air clean.
4- When we burn plastic that release horrible toxic chemicals in to the local environment.
5- Cigarettes contain addictive chemical called nicotine that causes all kinds of health problems.
6- Replacement of technological processes Le increases use of electricity, sunlight. Wind energy in place of coal.
Post a Comment