According to ODUM (1971), Pollution is “an undesirable change in the characteristics of air, water and land that harmfully affect the life and also create health hazards for all living organisms on the globe”.
According to SOUTHWICK (1976), Pollution can be defined as “the unfavorable (or) alteration of environment caused by human activities and causing harm to human beings”.
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Types of Pollution
Basically the Pollution is of two types viz.,
(1) Natural Pollution: This type of pollution is limited in its occurrence generally from natural
hazards like volcanic eruptions, emissions of natural gas, soil erosion, ultraviolet rays, cosmic
rays etc and
(2) Manmade Pollution: Most of the pollution is man made only. However, Pollution is usually
categorized as Air Pollution; Water Pollution; Thermal Pollution; Noise Pollution; Land & soil
Pollution; Radio Active Pollution and Marine Pollution
Air Pollution
Air pollution may be described as “the imbalance in quality of air so as to cause adverse effects on the living organisms existing on earth”. Pollution is due to the presence of undesirable substance of sufficient quantity which exists in environment. The substance or energy which causes pollution is called pollutant.
Types of air pollutants
Pollutants may be classified according to origin and state of matter.
a) According to Origin
Air pollutants are divided into two categories as primary & secondary.
1) Primary air pollutants are those which are emitted directly into the atmosphere. Eg: C; CO; CO2; SOx ; N; S; H; NOx; CFC’s etc .
2) Secondary air pollutants are those which are produced in the air by the interaction Among the primary air pollutants or by reaction with atmospheric constituents. Eg: Ozone (O3); Smog; Para Acetyl Nitrate (PAN); Acid Rain; Aerosols.
b) According to State of Matter
Air pollutants include fine solids; liquids and gases. Dust, Smoke, Fumes etc are examples for solid particles whereas fog is an example for liquid particles.
Primary Pollutants
1. Carbon Monoxide: It is a colorless, odorless, poisonous gas that is produced by the incomplete burning of carbon based fuels (coal, petrol, diesel and wood) which comes from the automobile industries, exhaust devices, About 70% of CO emissions are from the transport sector. When the air is polluted with CO, human blood is likely to be deprived of oxygen and leads to coma and death. In mild dosages, it leads to headache.
2. Oxides of Sulphur: SO2 is a gas produced from burning of coal, mainly in thermal power plants. Some industries such as paper mills produce SO2. It is injurious not only to men and plants, but it also attacks rapidly a few rocks such as limestone, marbles, electric contacts etc. It can even dissolve nylon.
Paper absorbs SO2 causing the paper to become brittle and fragile. SO2 polluted air leads to corrosion of metals such as Fe, Zn, Cu, steel etc… SO2 is a major contributor to Smog and acid rain. Sulphur trioxideis more irritant than SO2 because it combines immediately with water to form sulphuric acid.
3. Oxides of Nitrogen: Combustion of coal, oil, natural gas and gasoline which produces upto 50 ppm of Nitrogen. NOx are also produced when fossil fuels are burned especially in power plants and motor vehicles. NO2poisoning results SILOFILTER disease. High levels of NO2 exposure causes cough and make the human beings feel short of breath. People who are exposed to NO2 for a long time have a higher chance of getting respiratory infections. NOx compounds contribute for the formation of Ozone. Similarly, when nitrogen oxide when combine with SOx to form acid rain.
4. Chloro Fluoro Carbons: CFC’s (also known as Freon) are non- toxic. They contain Carbon, Fluorine and Chlorine atoms.The five main CFCs are the following: CFC – 11 (Trichloro Fluoro Methane CFCl3) CFC – 12 ( Dichloro Fluoro Methane CF2Cl2). The major uses of CFCs are as coolants in refrigerators and in air conditioners; as solvents in cleaners particularly for electronic circuit boards etc.. CFCs are the main cause of ozone depletion. CFCs have a lifetime in the atmosphere of about 20 to 100 years, and as a result one free chlorine atom from a CFC molecule can do a lot of damage.
Secondary Pollutants
1) Ozone (O3) / Ozone layer Depletion: Ozone consists of oxygen molecules which contain three oxygen atoms. It is not emitted directly into the air but produced in the atmosphere when oxygen combines with oxygen radical (O.) in the presence of sunlight. Ozone protects us from ultra violet radiation and other harmful rays.
It is observed that over the last few years, many manmade processes release gases into atmosphere causing drastic depletion of ozone layer. The chlorine atoms cause depletion of ozone slowly and holes are formed in the ozone layer. Ozone reacts with tissues and cause for breathing and decrease the working ability of the lungs, chest pains and coughing. It lowers the human body resistance power and leads to cold; pneumonia also.
Antarctic Ozone depletion: According to NIMBUS-7 satellite picture which was taken on 5th October, 1987 the protective ozone layer showed a hole over 50% of the area of the Antarctica continent covering 7 million sq km.
On Jan 1st 1989, the country Montreal (Canada) proposed redesigning refrigeration, air conditioning technology replacing the use of CFCs by ozone friendly substitutes.
2) Smog: Smog is a combination of smoke and fog or various gases when react in the presence of sunlight. The effects of smog on human health cause for respiratory, irritation to the eyes, diseases related to nose, throat, bronchitis, pneumonia, headache, nerves, liver, and kidneys. The first smog related deaths were recorded in London in 1873, when it killed 500 people. In 1892, December, London had worst experiences causing 1000 deaths. In 1940’s severe smog began covering the cities of Los Angeles in USA.
3) Acid rain: Acid rain has become one of the most important global environmental problems and poses significant adverse impact on soils, rivers, lakes, forests and monuments. The phenomenon occurs when SOx and NOx from the burning of fossil fuels such as Petrol, Diesel, Coat etc combine with water vapour in atmosphere and fall as rain or snow or fog. Natural sources like volcanoes, forest fires, etc also contribute SOx and NOx. Increased urban and industrial activities cause air pollution resulting in the rise of concentration of SO2 and NOx. Sulphur dioxide and NO2 combines with water vapour in the atmosphere produce sulphuric acid and Nitric acid respectively and results acid rain. Some of the examples are: Europe and parts of W Asia have experienced rain with water pH range of 4.5 to 5.0 (acidic) in 1958.
Air Pollution Effects, Prevention and Control Measures
Human beings breathe 22000 times a day on the average, inhaling 16 kg of air. Atmosphere constitutes a protective cover of gases surrounding the earth which sustains life and saves it from unfriendly environment.
The atmosphere consists of several layers viz. Troposphere, Stratosphere; Mesosphere; Thermosphere & Exosphere.
The lower atmosphere i.e., the troposphere contains 70% of gaseous components of major, minor and traces. Ultra violet radiation from the sun is absorbed by ozone in the stratosphere which is so called ozone layer located between 17 - 26 kms above sea level.
Effects of Air pollution
- The effects of pollution may be direct and affect certain organisms.
- The effects of pollution may possess a hazard or nuisance. Long continued pollution even affects the evolution of a species and eliminates organisms that cannot tolerate certain pollutants and favor others who can eat.
- Air pollution causes deaths, Impair health, reduce visibility and brings vast economic losses. It can also cause intangible losses to historic monuments such as Taj Mahal.
- Finally, Air pollution can affect the environment on a global scale.
Prevention and control of Air Pollution
- Inputs that do not contain the pollutants.
- Operating process to minimize generation of the pollutants.
- Replacing the process with one does not generate the pollutant.
- Removing the pollutants from the process.
- Substitution of raw materials.
Eg: The substitution of high sulphur coal with low sulphur coal in power plants.
Eg: Changing a fossil fuel with nuclear energy can eliminate sulphur emission. - By involving the Process Modification: Eg: Chemical and petroleum industries have changed by implementing Automated operations, computerized process control by reducing the Oxidation of SO2 to SO3 by reducing excess air.
- By involving the control technologies: Control equipment viz., Wet Collector (scrubber), Gravity Settling chamber; Cyclone Collectors, Dry Scrubbers, filters, electrostatic precipitators etc. are to be used to minimize the air pollution.