Substances that cause pollution of air are called as air- pollutants or atmospheric pollutants. These are fine Primary Pollutants that contribute more than 90 percent of global air pollution. These fine pollutants are carbon monoxide (CO); Nitrogen oxides (NOx); Sulphur oxides (Sox) and particulates. These pollutants can be put into two broad categories A. Gaseous Pollutants, and B. Particulates.
A – Gaseous Pollutants: The gaseous pollutants causing air pollution are numerous. Some remarkable gaseous pollutants in the present context are being mentioned below.
1. Sulphur dioxide: Sulphur dioxide (SO2) and sulphur tri- oxide (SO3) are produced largely by the combustion of coal and petroleum. These are also produced through smelting of ores of sulphide, copper, zinc, and lead; and decomposition of bio-mass. Some industries that emit sulphur dioxide are industries manufacturing sulphuric acid (H2SO4), oil refineries, fertilizer industries and paper industries.
2. Hydrogen sulphide: It is a colourless toxic gas which is produced from decaying vegetation and animal materials particularly in shallow fresh waters and marine environment. It also comes out from sulphur springs, volcanoes, coal pits and sewers.
3. Carbon monoxide: It is a poisonous gas which originates from incomplete combustion of carbonaceous materials. It can also be oxidized to carbon dioxide which too is a poisonous gas.
4. Hydrogen fluoride: It naturally comes out from volcanoes. However, it is produced from blast furnaces and industries concerned with the production of brick, tiles and super phosphates. It also comes out during combustion of coal.
5. Hydrogen chloride: It comes out during the combustion of coal, paper, plastics and chlorinated hydrocarbons.
6. Hydrocarbons: Chemical compounds made of hydrogen and carbon, are called as hydrocarbons. Methane, ethylene and aniline are three examples of hydrocarbons. Methane is the principal constituent of the natural gas. Major sources of release of hydrocarbons are organic matter, seepage from natural gas and oil fields and emissions of Volatile Organic Chemicals (VOCs). Hydrocarbons are also produced due to incomplete combustion of fuels, from Automobile exhausts, petroleum refineries, burning of crop residues, and cracking of natural gas in petrochemical plants etc.
Hydrocarbons undergo Photochemical Reactions in the atmosphere and sometimes produce a toxic substance known as Peroxy Acetyl Nitrate (PAN). PAN is a secondary pollutant which is found in Photochemical smog also. When the concentration of unburnt hydrocarbons increases in the atmosphere, it leads to the increase in the concentration of Ozone (O3) and NO2.
7. Ammonia: This gas is principally generated through refrigerator pre- cooler system of cold storage, manufacture of anhydrous ammonium fertilizers, nitric acid and domestic incineration, fertilizer plants etc. The leakage of ammonia from urea plants causes serious air Pollution in the factory area. Ammonia joins the atmosphere through leakage from the Urea plants also. The emission of ammonia causes bleaching of plant-leaves reduction of root and shoots growth, browning and softening of fruits, reduction in the rate of germination etc.
8. Nitrogen Oxides: Nitrogen oxide and Nitric Oxide are principal gaseous pollutants emitted through human activities. Nitrogen oxides have been reported to cause fading of colours of clothes, deterioration of nylon and cotton and corrosion of metals. Oxides of Nitrogen undergo Photochemical Reactions in the Mesosphere and Ionosphere. During this process the Photo dissociation of Nitrogen dioxide occurs to release one atom of oxygen which combines to form Ozone.
9. Tobacco Smoke: Smoking of cigarettes and allied things generate tobacco smoke. It is a potent pollutant in closed atmosphere like buses; trains etc. It causes lung cancer, pulmonary and coronary heart diseases. Even passive smokers may be caught by a pulmonary or a coronary disease.
10. Photochemical Oxidants: Substances that are reactive in the presence of sunlight and form oxides of different substances present in the atmosphere are called as Photochemical Oxidants. SOx, NOx, PAN, PB2N, Peracetic Acid, Acetyl peroxide are some examples of Photochemical Oxidants. Most of these substances are produced by automobiles.
B – PARTICULATES
Solid and liquid aerosols that remain suspended in the atmosphere are called as particulates. Particulates can be defined as non-gaseous concentrations in the atmosphere. Hence these cannot be expressed in volume units. Their size is usually measured in microgram per cubic meter (µg/m3). 1 microgram (1µg) is equal to 0.00000004 oz. The typical sizes of atmospheric particulates range from 0.1µm to 1µm. These are small solid particles and liquid droplets that can pose serious threat to the quality of air. Smoke, dust, mist, sprays, chlorofluorocarbons (CFCs), fumes etc. are some examples of particulates. Particulates are produced by human activities related to condensation or dispersion. The particulate matter can produce toxicity and respiratory problems like bronchitis and emphysema. Fluorides, lead, cement dust, potassium salts, smoke particles, plant spores, bacteria etc. are example of some other particulates.
Particulates may be organic or inorganic by chemical nature. Organic particulates originate from the combustion of fuels, automobiles and vegetation. Some of the organic particulates are Polycyclic Aromatic Hydrocarbons (PAHs), Aldehydes, Ketones, Peroxides, Esters and Oxidised and Polymerised Hydrocarbons etc. Inorganic Particulates originate from metallic oxides, sulphides and carbonates etc. These are produced on burning of fuels containing metals. Oxides of iron, vanadium, lead etc. are some of the inorganic particulates found in the sample of polluted air.
Particulate Matter found in air can be classified on the basis of the size of particles also. Those particulates which can be inhaled easily by human beings are called as Respirable Particulate Matter (RSPM). However, some particulates consist of bigger particles and hence can not be and must not be inhaled through air. Such particulates are called as Non-Respirable Particulate Matter.
Particulate matter present as pollutant in the air can be put into different groups like dust, smoke, soot, aerosols, fumes, smog, haze and mist.
1. Dust: Particles of different sizes (from 1 micron to 200 microns) produced due to crushing of stones, weathering of rocks and digging of upper crust of the earth are called as dust. The dust particles are blown away and lifted up in air due to stormy conditions of atmosphere. However, they settle down due to gravitational pull of the earth or are washed down by rain water.
2. Smoke: Fine carbon particles (0.50 to 1 micron) along with gases produced due to the incomplete combustion of organic matter is called as smoke.
3. SOOT: Bigger particles of carbon (1 to 10 micron) hanging in air along with tar, are called as soot.
4. Aerosol: Fine particles of solids, liquids or gases suspended in air are called as aerosol.
5. Fumes: Particles of gaseous pollutants (0.08 to 1 micron) in the state of condensation are called as fumes. Traces of Nitrogen Oxides and Sulphuric Oxides, Carbon Tetra Chloride (CCl4), Chlorofluorocarbons (CFCs) etc. are released through human activities and are found in the upper atmosphere as aerosols.
6. Smog: Mixture of smoke particles and vapours of liquids formed due to photo- chemical reactions in the atmosphere is called as smog or photochemical smog. It is mainly formed due to secondary pollutants like NO2, O3, aldehydes, aerosols and PAN. It reduces visibility and often causes a serious health hazard.
7. Haze: Dust particles and water vapours present in air so as to reduce visibility, is called as haze.
8. Mist: The suspension of liquid particles in air ranging from 40 to 500 microns is called as mist.
Noise Pollution
Sound without value is called as noise. The Noise Pollution can be defined as the unwanted sound which gets dumped into the atmosphere without taking care of any adverse effect that may be produced by it. It is the sound which is undesired by the recipient. The most dangerous part of air pollution is Noise Pollution. Since, sound needs the medium of air, the noise pollution can also be taken up with the air pollution.
Causes of Noise Pollution
Pressure horns of cars and other vehicles, noise produced through loud speakers during social and religious functions, noise produced by heavy machines, irresponsible practice of hearing high pitched sound of music systems, televisions etc. are some remarkable sources of noise pollution.
Measurement of Noise and Hearing Capacity
The popular unit of sound measurement is decibel (dB) which is the tenth part of a Bell. This unit has been named after Sir Alexander Graham Bell. The human ear is sensitive to sound from 0 to 180 dB. However, the sound beyond 80 dB is harmful and the threshold for pain, tissue damage, and potential loss of hearing in humans is 120 decibels. Decibel (dB) is a ratio expressed as the logarithmic scale relative to the pressure level of a reference sound. It is the tenth part of the largest unit Bel. The instrument used to measure intensity of sound is called as Decibel meter.
Human ear is capable of hearing sound of varying frequencies and intensities. However, sound or noise of 115 to 180 dB is harmful and sometimes fatal to human beings. There are people who cannot tolerate sound of even the intensity of 85 dB whereas there are people who can tolerate the sound of the intensity of even up to 115 db. After all, the sound of the intensity above 145 dB is painful and damaging to everyone.
Impacts of Noise Pollution
Noise interferes with communication, relaxation, leisure, heartbeat, eardrum and mental conditions. It is very harmful to sick persons and students who remain on their studies. Hence, noise is considered as serious pollutant which spreads through the air. In brief, the impacts of noise pollution are listed below-
(i) It causes repeated interference with sleep and noisy conditions have very harmful impacts on the mental conditions of the people.
(ii) Continuous exposure to noise levels above 100 dB causes deafness and mental tension.
(iii) High-pitched sound interferes with conversations of people,
(iv) Noise pollution reduces work efficiencies of people,
(v) It causes considerable damage to the mental and physical health of the people. It causes cardiovascular problems like heart disease and high blood pressure,
(vi) It causes social conflicts at home and work place.
Prevention of Noise Pollution
The Noise Pollution can be prevented and Controlled by several important practices. However, the control of noise pollution is not an easy task. At community level, it can be controlled by applying civic sense by the polluters themselves. The district administration and the State Pollution Control Boards fix the range of intensity of sound produced by someone or by industry through legal ways. We can avoid noise pollution by soundproofing or by insulating our houses. The following table details the different types and ranges of sound.
