Causes of Air Pollution:
Pollution is an undesirable change in the physical, chemical or biological characteristics of air, water and soil that may harmfully affect the life or create a potential health hazard of any living organism. Pollution is thus direct or indirect changes in any component of the biosphere that is harmful to the living component(s), and in particular undesirable for man, affecting adversely the industrial progress, cultural and natural assets or general environment.watch Causes of Air Pollution to learn more.
It is defined as the excessive concentration of foreign material in the atmosphere , which affects the health of individuals and also causes damage to the property. Air pollution episodes • London smog : SO2 à H2SO3 vapours in the atmosphere. When automobile exhausts are trapped by this smog and exposed to sunlight, it produces photochemical smog. • Bhopal gas tragedy : The poisonous gas, methyl isocyanate (MTC) leakage in the pesticide manufacturing plant of Union Carbide of India Ltd., (UCIL), Bhopal, Madhya Pradesh on December 3, 1984. 46 tons of MIC was released spreading to 40 km. Effects : About 65,000 people suffered from various disorders in eyes, lungs, stomach, heart, etc. The immediate symptom is bronchospasm which causes coughing, chest pain and abdominal pain. Nearly 3000 people died within a short span of time, 1600 domestic animals died and crop yields were reduced . • Darkening effect of Taj Mahal Taj Mahal is a white marble stone mausoleum. Recently it was observed that the walls of Taj Mahal has become darkened and disfigured due to air pollution from nearby Mathura Oil refinery. H2O + SO2 à H2SO3 , SO2 + O2 à SO3; SO3 + H2O à H2SO4. The acid rain reacts with marble stone (CaCO3) to produce calcium sulphate, causing darkening and disfigurement. Types, sources and effects of air pollution Air pollution may be simply defined as the presence of certain substances in the air in high enough concentrations and for long enough duration to cause undesirable effects. “Certain substances” may be any gas, liquid or solid, although certain specific substances are considered significant pollutants because of very large emission rates are harmful and unwanted effects. “Long enough durations” can be anywhere from a few hours to several days or weeks; on a global scale, durations of months and years are of concern.
Causes of Air Pollution Due to Industry:
Sources Air pollution results from gaseous emission from mainly industry, thermal power stations, automobiles, domestic combustion etc. 1. Industrial chimney wastes: There are a number of industries which are source of air pollution. Petroleum refineries are the major source of gaseous pollutants. The chief gases are SO2 and NOx. Cement factories emit plenty of dust, which is potential health hazard. Stone crushers and hot mix plants also create a menace. Food and fertilizers industries which emit gaseous pollutants. Chemical manufacturing industries which emit acid vapours in air. 2. Thermal power stations: There are a number of thermal power stations and super thermal power stations in the country. The National thermal power corporation (NTPC) is setting up four mammoth coal-powered power stations to augment the energy generation. These are at Singrauli in U.P., Korba in M.P., Ramagundam in Andhra Pradesh and Farakka in W. Bengal. The coal consumption of thermal plants is several million tones. The chief pollutants are fly ash, SO 2 and other gases and hydrocarbons. 3. Automobiles: The toxic vehicular exhausts are a source of considerable air pollution, next only to thermal power plants. The ever increasing vehicular traffic density posed continued threat to the ambient air quality. Chief sources of emission in automobiles are (i) exhaust system, (ii) fuel tank and carburettor and (iii) crankcase. The exhaust produces many air pollutants including unburnt hydrocarbons, CO, NOx and lead oxides. There are also traces of aldehydes, esters, ethers, peroxides and ketones which are chemically active and combine to form smog in presence of light. Evaporation from fuel tank goes on constantly due to volatile nature of petrol, causing emission of hydrocarbons. The evaporation through carburettor occurs when engine is stopped and heat builds up, and as much as 12 to 40 ml of fuel is lost during each long stop causing emission of hydrocarbons. Criteria Air Pollutants The five primary criteria pollutants include the gases- Carbon Monoxide (CO), nitrogen oxides (NOx) , sulfur dioxide (SO2), and solid or liquid particulates (smaller than 10 µm), and particulate lead. a) Carbon Monoxide 6 • CO is a colourless, odourless and tasteless gas. • It is produced when carbonaceous fuels are burned under less than ideal conditions. • Incomplete combustion, yielding CO instead of CO2, results when any of the following variables are not kept sufficiently high: i. Oxygen supply ii. flame temperature iii. gas residence time at high temperature and iv. combustion chamber turbulence. • Most of the CO emissions are from the transportation sector. Hourly atmospheric concentrations of CO often reflect city driving patterns. Peaks occur on week days during the morning and late afternoon rush hours. • The CO, at levels that occur in urban air has no detrimental effect on materials or plants; but adversely affects human health. • CO interferes with the blood’s ability to carry oxygen to the cells of the body. When inhaled, it readily binds to hemoglobin in the blood stream to form carboxyhemoglobin (COHb). • Even small amounts of CO can seriously reduce the amount of oxygen conveyed throughout the body à brain function is affected and heart rate increased in an attempt to offset the oxygen deficit. b). Oxides Of Nitrogen • 7 oxides of nitrogen are known to occur – NO, NO2, NO3, N2O, N2O3, N2O4 and N2O5. • Nitric oxide (NO) and Nitrogen dioxide (NO2) are important in air pollution study.watch Causes of Air Pollution to learn more.
Useful for CBSE, ICSE, NCERT & International Students
Grade : 8
Subject : Chemistry
Lesson : Air
Topic: Causes of Air Pollution
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