{"id":235,"date":"2019-03-07T07:24:14","date_gmt":"2019-03-07T07:24:14","guid":{"rendered":"http:\/\/esp16.epgpbooks.inflibnet.ac.in\/?post_type=chapter&p=235"},"modified":"2019-04-25T07:17:14","modified_gmt":"2019-04-25T07:17:14","slug":"air-pollution","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/esp16\/chapter\/air-pollution\/","title":{"rendered":"Air Pollution"},"content":{"raw":"
\"epgp<\/a>\r\n<\/span><\/div>\r\n \r\n\r\n \r\n\r\nContents<\/strong>\r\n
    \r\n \t
  1. What is Air Pollution?<\/li>\r\n \t
  2. Classification of Pollutants<\/li>\r\n \t
  3. Sources of Pollutants<\/li>\r\n \t
  4. Criteria Air Contaminants(CAC) or Criteria Pollutants<\/li>\r\n \t
  5. Processes Responsible for Air Pollutants<\/li>\r\n \t
  6. Sources of Sulfur Dioxide<\/li>\r\n \t
  7. Natural Sources<\/li>\r\n \t
  8. Anthropogenic Sources<\/li>\r\n \t
  9. Control of Carbon Monoxide Pollution<\/li>\r\n \t
  10. Urban Air Pollution<\/li>\r\n \t
  11. Monitoring of Carbon Monoxide and Smoke<\/li>\r\n \t
  12. Regional & Global Pollution<\/li>\r\n \t
  13. Indian Air Quality Standards<\/li>\r\n \t
  14. Basis of Air Quality Regulations<\/li>\r\n \t
  15. Components of Air Quality Standards<\/li>\r\n \t
  16. Objectives of Indian Ambient Air Quality Standards<\/li>\r\n \t
  17. References<\/li>\r\n<\/ol>\r\nWhat is Air Pollution?<\/strong>\r\n\r\nAir pollution occurs, when harmful and toxic gases, dust and smoke, etc, enter the atmosphere.\r\n\r\n \r\n

    \u00a0 \u00a0These make the survival of humans, plants and animals difficult and also disfigure the buildings and lead to deterioration of assets.According to Brimblecombe (1996), air pollution occurs when the substances are released into the air by human activities in such concentrations as are sufficient to cause detrimental effect on human health, vegetation, animals and property or interfere with the enjoyment of the property by the mankind. So the contamination of air whether inside or outside the house is the cause of air pollution. These cause physical, biological or chemical changes in air, which if harmful, cause air pollution. The composition of air is given in Table 1<\/p>\r\n \r\n\r\nTable 1. <\/strong>Composition of dry unpolluted air (Brimblecombe, 1996, Girard, 2011).\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
    Gases<\/strong><\/td>\r\nPer cent<\/strong><\/td>\r\n<\/tr>\r\n
    Nitrogen<\/strong><\/td>\r\n78.084%<\/strong><\/td>\r\n<\/tr>\r\n
    Oxygen<\/strong><\/td>\r\n20.946%<\/strong><\/td>\r\n<\/tr>\r\n
    Argon<\/strong><\/td>\r\n0.934$%<\/strong><\/td>\r\n<\/tr>\r\n
    Carbon dioxide<\/strong><\/td>\r\n0.039%<\/strong><\/td>\r\n<\/tr>\r\n
    Neon<\/strong><\/td>\r\n0.0018%<\/strong><\/td>\r\n<\/tr>\r\n
    Helium<\/strong><\/td>\r\n0.000526%<\/strong><\/td>\r\n<\/tr>\r\n
    Methane<\/strong><\/td>\r\n0.00016%<\/strong><\/td>\r\n<\/tr>\r\n
    Krypton<\/strong><\/td>\r\n0.00005%<\/strong><\/td>\r\n<\/tr>\r\n
    Hydrogen<\/strong><\/td>\r\n0.00003%<\/strong><\/td>\r\n<\/tr>\r\n
    Nitrous oxide<\/strong><\/td>\r\n0.00003%<\/strong><\/td>\r\n<\/tr>\r\n
    Ozone<\/strong><\/td>\r\nTrace to 0.0008%<\/strong><\/td>\r\n<\/tr>\r\n
    Carbon monoxide<\/strong><\/td>\r\nTrace to 0.000025<\/strong><\/td>\r\n<\/tr>\r\n
    Sulfur dioxide<\/strong><\/td>\r\nTrace to 0.00001%<\/strong><\/td>\r\n<\/tr>\r\n
    Nitrogen dioxide<\/strong><\/td>\r\nTrace to 0.000002%<\/strong><\/td>\r\n<\/tr>\r\n
    Ammonia<\/strong><\/td>\r\nTrace to 0.0000003%<\/strong><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n \r\n

    \u00a0 \u00a0It is remarkable to note that the concentration of pollutant gases is less than 0.1% but their toxic effects are highest. Out of the list in Table 1, the pollutant gases are tropospheric ozone, nitrogen oxides, sulfur dioxide, carbon monoxide, ammonia, methane, etc.<\/p>\r\n \r\n\r\nClassification of Pollutants<\/strong>\r\n

    The pollutants can be classified in distinct groups in a variety of ways, some of which are follows.<\/p>\r\n \r\n

      \r\n \t
    1. Primary Pollutants<\/strong><\/li>\r\n<\/ol>\r\n

      These are released directly into the air from the source. Based on physical state<\/strong>, these are classified as follows.<\/p>\r\n(i) Gaseous Primary Pollutants<\/em><\/strong>\r\n

      Some of the gaseous pollutants are as follows.<\/p>\r\n

      (a) Sulfur dioxide, SO2<\/p>\r\n

      (b) Nitrogen oxides, NOx<\/em>. ( NOx = NO + NO2<\/span><\/p>\r\n

      (c) Hydrocarbons(CH4, propane, ethylene, etc); volatile organic compounds(VOCs); polycyclic aromatic hydrocarbons(PAHs), and large number of other organic compound<\/p>\r\n

      (d) Carbon monoxide, CO<\/p>\r\n

      (e) Tropospheric ozone, O3<\/p>\r\n

      (f) Carbon dioxide, CO2, chlorofluorocarbons (CFCs), halons, nitrous oxide, N2 Although these pollutants as such do not have any detrimental effect but are implicated in global climate change.<\/p>\r\n \r\n\r\n(ii) Primary Aerosols<\/strong>\r\n

      \u00a0 \u00a0Aerosols are dispersions of solid \/liquid particulates in air. The primary particulates like soil particles, fly ash , smoke etc. are directly released in air<\/p>\r\n \r\n\r\nDepending on the source\/origin air pollutants are classified as<\/strong>\r\n

        \r\n \t
      1. a) Primary air pollutants and b) Secondary air pollutants<\/em><\/li>\r\n<\/ol>\r\n \r\n
          \r\n \t
        1. a) <\/strong>Primary air pollutants<\/strong><\/li>\r\n<\/ol>\r\n

          \u00a0 \u00a0Primary air pollutants are those that are emitted directly from the identifiable sources. The examples of primary air pollutants:<\/p>\r\n

          \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 i) Carbon monoxide<\/p>\r\n

          \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0ii) NOx ( oxides of nitrogen<\/p>\r\n

          \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 iii) SOx ( oxides of sulphur)<\/p>\r\n

          \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 iv) Hydrocarbons<\/p>\r\n

          \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 v) Particulate matter<\/p>\r\n\r\n

            \r\n \t
          1. b) Secondary air Pollutants<\/strong><\/li>\r\n<\/ol>\r\n

            \u00a0 \u00a0The pollutants that are produced by the interaction among two or more primary air pollutants in the air or by reaction with constituents of air. These pollutants are formed in air due to the photochemical and thermal reactions of primary pollutants. For example, aerosols, ground level ozone, peroxyacetyl nitrate (PAN), tropospheric ozone, acid rain, photochemical smog are the pollutants of this type.<\/p>\r\n \r\n

            \u00a0 \u00a0 \u00a0 \u00a0(i)\u00a0 Secondary Gaseous Pollutants<\/em><\/strong><\/p>\r\n

            \u00a0 \u00a0These are generated in air through chemical reactions. Some of these are as follows:<\/p>\r\n\r\n

              \r\n \t
            1. Tropospheric ozone, O3.<\/li>\r\n \t
            2. Aldehydes.<\/li>\r\n \t
            3. Peroxyacetylnitrate etc.<\/li>\r\n<\/ol>\r\n

              \u00a0 \u00a0 \u00a0 \u00a0 \u00a0(ii) <\/em><\/strong>Secondary Aerosols<\/em><\/strong><\/p>\r\n

              \u00a0 \u00a0These are formed in air, mostly through gas to particulate conversion, e.g., SO2 to sulfate aerosol, NOx to nitrate aerosols, ammonia into ammonium sulfate aerosol, VOCs into carbonaceous particles etc.<\/p>\r\n \r\n\r\nSource \u2013 Dependent Classification of Aerosols<\/strong>\r\n\r\nBased on the origin of aerosols, these are classified as follows.\r\n\r\n \r\n\r\n\u00a0 (i) <\/em>Biological Aerosols<\/em><\/strong>\r\n

              These\u00a0 are\u00a0 of\u00a0 biological\u00a0 origin,\u00a0 viz.,\u00a0 seeds,\u00a0 pollens,\u00a0 spores,\u00a0 fragments\u00a0 of\u00a0 plants\/ animals\/insects, hair, bacteria, fungi, micro-organisms, algae, protozoa, viruses etc.<\/p>\r\n(ii) Geochemical Aerosols<\/em><\/strong>\r\n

              These aerosols are made up of geo-chemicals and are directly injected into air due to volcanic eruptions, mining, crushing, blasting, dispersion of dust through wind or human activities.<\/p>\r\n(iii) Oceanic Aerosols<\/em><\/strong>\r\n\r\n(iv) Anthropogenic Aerosols<\/em><\/strong>\r\n

              Fossil fuel combustion, biomass burning, industrial activities, e.g., manufacturing and metallurgical processes , cement plants etc. are some of the big sources. Automobiles are other big sources of this type of aerosols.<\/p>\r\n(v) <\/strong>Other Sources of Aerosols<\/em><\/strong>\r\n\r\nSome other sources of aerosols are forest fires and meteoritic debris.\r\n\r\n \r\n\r\nChemical Composition \u2013 Based Classification of Aerosols<\/em><\/strong>\r\n\r\nBased on chemical composition the aerosols are classified as follows.\r\n\r\n \r\n\r\n(i) Inorganic Aerosols<\/em><\/strong>\r\n\r\nBasically, these are made from inorganic compounds and further divided in two categories\r\n

              \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0Soluble Aerosols<\/strong>: These are soluble in water. The aerosols of salts like NaCl, and (NH4)2SO4 are of this type.<\/p>\r\n\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0Insoluble Aerosols<\/strong>: The examples of aerosols this type include those derived from minerals, stones, etc. These are not soluble in water.\r\n\r\n \r\n\r\n(ii) Organic Aerosols<\/em><\/strong>\r\n

              These are made from organic compounds. Examples are carbonaceous particles, polycyclic hydrocarbons(PAHs), soot, etc<\/p>\r\n \r\n\r\nSources of Pollutants<\/strong>\r\n

              There are innumerable sources of air pollutants, some known and some unknown. According to Phalen and Phalen (2013), these sources can classified in many ways as mentioned below<\/p>\r\n \r\n

              (i) Natural Sources: <\/strong>The natural processes such as volcanoes, lightning, storms, etc, fall\u00a0 in this category.<\/p>\r\n(ii) Anthropogenic Sources<\/strong>: Human activities constitute manmade or anthropogenic\r\n

              (iii) Secondary Sources<\/strong>: The processes of formation of pollutants in atmosphere due to reactions of natural and manmade pollutants are secondary sources.<\/p>\r\n \r\n\r\nPollutant sources have been categorized in following manner also.\r\n\r\n(i) Stationary Sources<\/strong>: Such as homes, factories, power plants, etc.\r\n

              (ii) Mobile Sources<\/strong>: Such as vehicles, trains, aircrafts, ships, tractors, etc.<\/p>\r\n \r\n

              A further subdivision of pollutants as given below has also been proposed.<\/p>\r\n \r\n\r\n(i) Indoor Pollutant Sources<\/strong>: Such as kitchen\r\n\r\n(ii) Outdoor Pollutant Sources:<\/strong> The sources outside the homes\r\n\r\n(iii) Point Sources:<\/strong> Highly localized such as power plants, factories.\r\n\r\n(iv) Distributed Sources<\/strong>: Such as agricultural operations and cities\r\n\r\n(v) Local Sources:<\/strong> such as power plants\r\n\r\n(vi) Global Sources<\/strong>, Dust, soil, biological processes, volcanoes\r\n\r\n(vii) Inorganic Sources<\/strong>. Soil, etc.\r\n\r\n(viii) Organic Sources,<\/strong> Agricultural processes, etc.\r\n\r\n \r\n\r\nCriteria Air Contaminants (CAC) or Criteria Pollutants<\/strong>\r\n

              \u00a0 \u00a0A set of six most common air pollutants, viz., carbon monoxide, nitrogen dioxide, lead, ozone, sulfur dioxide and particulate matter selected by US Environmental Agency that cause smog, acid rain and other health hazards, are called criteria air contaminants. These are generally emitted by sources in industry, transportation, mining, electric generation, agriculture. Mostly these are produced by combustion of fossil fuels or industrial processes. These substances have defined allowable concentrations in ambient air as per national air quality standard. This national quality standard has to be revised every five year. These contaminants are considered to present a general risk to the health of the public.<\/p>\r\n \r\n\r\nHazardous Pollutants<\/strong>\r\n

              \u00a0 \u00a0US EPA has another list of about 200 substances, which are believed to cause adverse health or environmental effects. This list includes compounds such as benzene, asbestos, arsenic and nickel compounds, formaldehyde, radionuclides etc. This list can undergo change at any time.<\/p>\r\n \r\n\r\nProcesses Responsible for Air Pollutants<\/strong>\r\n

              \u00a0 \u00a0Brimblecombe (1996) has categorized the anthropogenic processes responsible for the formation and release of pollutants in atmosphere as follows.<\/p>\r\n\r\n

                \r\n \t
              1. Combustion of Fuels:\u00a0\u00a0<\/strong>Combustion of fossil fuels, such as coal, petroleum products, hydrocarbons, etc. is the most significant source of pollutants. The pollutants released are CO2 - major culprit of global warming, carbon monoxide, sulfur dioxide, unburnt hydrocarbons, nitrogen oxides, polycyclic aromatic hydrocarbons(PAHs), etc. The toxic metals in different chemical forms are also released.<\/li>\r\n<\/ol>\r\n
                  \r\n \t
                1. Incineration:\u00a0<\/strong>\u00a0 Incineration of municipal waste, which contains chlorine compounds, such as polyvinylchloride, present as impurity is a source of HCl, CH3Cl, etc. Possibly, it is a source of several highly toxic and carcinogenic chlorinated dioxins and furans.<\/li>\r\n<\/ol>\r\n
                    \r\n \t
                  1. High Temperature Sources:\u00a0\u00a0<\/strong>The metallurgical processes such as smelting and brick making are high temperature sources, which release pollutants such as carbon dioxide( manufacture of cement), sulfur dioxide(smelting of sulfide ores), toxic metals like arsenic(present as impurity), hydrogen fluoride( brick making and cryolite smelting for production of aluminum), etc.<\/li>\r\n<\/ol>\r\n
                      \r\n \t
                    1. Evaporation of Volatile Organic Compounds(VOCs):\u00a0\u00a0<\/strong>It is considered a low temperature source. The evaporation of VOCs takes place from solvent use, petroleum industries, etc. Mining and gas leakage are other sources. The use of pesticides in agriculture is a worrisome source of toxic organic compounds. In the next section, the sources of individual pollutants in somewhat detail are discussed.<\/li>\r\n<\/ol>\r\n \r\n\r\nSources of Sulfur Dioxide<\/strong>\r\n\r\nNatural Sources<\/em><\/strong>\r\n

                      \u00a0 Volcanoes and oxidation of sulfur gases produced by decomposition of plants are the important natural sources of sulfur dioxide. Other sources are sulfur- based hot springs and geysers. Since the natural sulfur dioxide by volcanoes is released high in the atmosphere, and by other sources at far from the populated areas, its background concentration remains low (about 1 ppb).<\/p>\r\n \r\n\r\nAnthropogenic Sources<\/em><\/strong>\r\n\r\n(i) <\/strong>Coal Combustion<\/em><\/strong>\r\n

                      \u00a0 \u00a0Coal combustion is the biggest manmade source of atmospheric SO2. Depending upon the area from which coal is mined, it contains 1-9% sulfur. This sulfur is present in two forms. About half of the sulfur is present as inclusions in the mineral content of the coal. By pulverizing the coal before combustion, this sulfur can be removed mechanically. The remaining sulfur is a part of coal matrix and is bonded in the complex coal structure. Removal of this sulfur requires complex and costly processing.<\/p>\r\n \r\n\r\n(ii) Petroleum<\/em><\/strong>\r\n

                      \u00a0 \u00a0Crude oil contains few percent of sulfur. However, during refining it is reduced to few ppm in gasoline. Refining is responsible for the release of some SO2 in the atmosphere.<\/p>\r\n \r\n\r\n(iv)Natural Gas<\/em><\/strong>\r\n

                      \u00a0 \u00a0Natural gas also contains sulfur compounds, mainly H2S. The cleaning of natural gas is responsible for the release of some H2S.<\/p>\r\n \r\n\r\n(iii) Smelting<\/strong>\r\n

                      \u00a0 \u00a0Many metals such as nickel and copper occur in nature in the form of sulfide ores. When these ores are roasted, sulfur is oxidized and SO2 is formed. The sulfur dioxide so formed may be\u00a0\u00a0\u00a0 obtained in the liquefied form or converted to H2SO4.<\/p>\r\n \r\n\r\n(iv) Paper and Pulp Manufacture<\/strong>\r\n

                      \u00a0 \u00a0Wood pulping uses hot sulfite is used in wood pulping and so the process releases some SO2. Is H2S, which on oxidation forms SO2, is released by kraft pulping process.<\/p>\r\n \r\n\r\nSources of Carbon Monoxide<\/strong>\r\n

                      \u00a0 \u00a0CO is a tasteless and odorless gas. Because of latter property, one is unable to feel\/<\/strong>recognize its inhalation, which may result in death.<\/p>\r\n \r\n\r\nNatural Sources<\/strong>\r\n

                      \u00a0 \u00a0The natural sources are oxidation of methane, terpenes, isoprene, forest fires, lightning, seed germination, etc. Its background concentration is ~ 100 ppb and it is the most abundant criteria air contaminant(CAC).<\/p>\r\n \r\n\r\nAnthropogenic Sources<\/strong>\r\n

                      \u00a0 \u00a0The major manmade sources are industrial units and automobiles which produce CO due to incomplete combustion of carbon containing fuels. Complete oxidation of carbon produces CO2. The incomplete combustion due to insufficient oxygen is responsible for some partial oxidation of carbon.<\/p>\r\n

                      \"\"\u00a0 \u00a0In carbon containing high temperature processes, such as smelting of iron in blast furnace, carbon reacts with CO2 to produce large amount of CO.<\/p>\r\n

                      \"\"\u00a0 \u00a0The incomplete combustion of hydrocarbon fuels in automobiles is the most significant source of CO pollution in urban areas. For pure octane the correct air to fuel(AFR) ratio is 14.7. Actually this ratio depends upon the composition of fuel, which is a mixture of several hydrocarbons and may have some oxygenate organic compounds also. If the mixture is rich (more fuel), there is insufficient oxygen to completely oxidize carbon into CO2, resulting in the formation and emission of CO. On the other hand if the AFR is higher than stoichiometric amount, the mixture is considered lean. Lean mixtures are more efficient in ensuring nearly complete oxidation of carbon into CO2 but produce higher levels of nitrogen oxides.<\/p>\r\n \r\n\r\nControl of Carbon Monoxide Pollution<\/strong>\r\n

                      \u00a0 \u00a0The automobiles are the sources of many notorious pollutants. Therefore, the techniques to control CO formation in internal combustion engine, and to convert CO formed in to CO2 before release are employed. The use of three-way catalytic converters in automobiles is now mandatory to control the air pollution. It is so named because it simultaneously reduce the amounts of CO, hydrocarbons and NOx. It consists of a ceramic honeycomb, impregnated with catalysts platinum, palladium and rhodium. It has two chambers. Engine gases containing CO, NOx and HC enter the chamber. At the surface of the catalyst, reaction of hydrocarbons(HC) with water produces H2. Rhodium catalyzes the reduction of NO by H2.<\/p>\r\n \r\n

                      \"\"\u00a0 \u00a0Then excess air is pumped into exhaust stream to make available oxygen, which on catalysis by Pt and Pd, oxidizes CO in to CO2 and HC into CO2 and H2O.<\/p>\r\n

                      \u00a0 \u00a0The major natural sink of CO in atmosphere is the oxidation of CO by OH radicals into CO2. Soil microorganisms also remove CO.<\/p>\r\n \r\n\r\nGround Level Ozone<\/strong>\r\n\r\nThe major source of ozone is photochemical reactions in troposphere as discussed in a subsequent module.\r\n\r\n \r\n\r\nVolatile Organic Compounds\/Hydrocarbons<\/strong>\r\n\r\nThe detailed atmospheric chemistry including sources are presented in a separate Module on VOC.\r\n\r\n \r\n\r\nUrban Air Pollution<\/strong>\r\n

                      \u00a0 \u00a0There has been a massive growth in the size and the population of the cities, in particular, in developing countries. An endless stream of automobiles is being added each year. This has led to deterioration in the quality of air in the cities and neighboring areas. The air pollution has increased. The urban air pollution is an important factor in changing the climate of cities.<\/p>\r\n \r\n\r\nThe following urban characteristics seriously affect the urban climate.\r\n

                        \r\n \t
                      1. Creation of urban heat islands<\/li>\r\n \t
                      2. Lower average wind speeds<\/li>\r\n \t
                      3. Increase in fog frequency<\/li>\r\n \t
                      4. Changes in the vertical structure of the lower boundary layer<\/li>\r\n \t
                      5. Formation of meso-scale circulation systems, etc<\/li>\r\n<\/ol>\r\n

                        \u00a0 \u00a0The major pollution factors, which are briefly discussed below, are waste heat, sulfur dioxide, carbon monoxide, nitrogen oxides, hydrocarbons\/organic compounds, photochemical oxidants and suspended particulate matter.<\/p>\r\n \r\n\r\nWaste Heat<\/strong>\r\n

                        \u00a0 \u00a0Waste heat is an important aspect of urban temperature and moisture content. It is unique to urban environments due to dense network of sources of heat. It is likely to aid in the formation of secondary pollutants.<\/p>\r\n \r\n\r\nSources of waste heat<\/em><\/strong>\r\n\r\nAutomobiles and transportation exhausts\r\n\r\nIndustrial emissions\r\n\r\nPower plant plumes.\r\n\r\nDomestic heating\/<\/strong>cooking\r\n\r\nAir conditioning\r\n\r\n \r\n

                        Excess heat stored in buildings, pavements, roads and other structures which heat up fast<\/p>\r\n

                        \u00a0 \u00a0In urban centers due to lack of plant cover only small fraction of this heat is used for evapo-transpiration. Most of the heat is released as sensible heat and small portion as infrared radiation and latent heat. In India waste heat influence is most noticeable in summers.<\/p>\r\n \r\n

                        \u00a0 \u00a0The waste heat flux is determined largely by density of sources. The average heat released by cities shows the large spatial variation. For example, the annual heat released by Manhattan city has been reported to be about 17.4 GW (in summer) and 21.8 (in winter). The heat fluxes varied widely from 5 W\/m2 on the urban fringes to >100 W\/m2 in the city centre. These values are large when compared with annual average net radiation balance at earth surface in mid - latitude of about 100 W\/m2. Thus, the cities add a significant portion of artificial heat to radiation balance.<\/p>\r\nObviously, the temperature in the city is likely to be higher than the surrounding areas.\r\n\r\nHowever, the total contribution of cities to earth radiation balance on global scale is negligible.\r\n\r\nNevertheless, at the local scale this is serious.\r\n\r\n \r\n\r\nAutomobile Exhaust Emissions<\/em><\/strong>\r\n\r\nThe major pollutants released by automobile exhaust are as follows.\r\n

                          \r\n \t
                        1. Carbon monoxide, CO. <\/em>It is the most abundant pollutant in urban areas. It is formed due to incomplete combustion of carbonaceous fuels. The correct air to fuel ratio is ~ 14.5. If the mixture is rich (more fuel), there is insufficient oxygen to completely oxidize carbon into CO2 resulting in the formation and emission of CO.<\/li>\r\n \t
                        2. Unburnt hydrocarbons. <\/em>In urban areas the exhaust emissions, evaporative losses from fuel tank, carburetor etc. are the major sources of polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs). Many of these are highly toxic and carcinogenic. Ethylene is produced in petrol engines due to use of ethylene dibromide and dichloride.<\/li>\r\n \t
                        3. Sulfur Dioxide, SO<\/em>2<\/em> .This is formed due to oxidation of sulfur present in fuel.<\/li>\r\n \t
                        4. Organic \/ Inorganic Lead \u2013 Compounds. <\/em>Use of tetraethyllead(TEL)( now banned) as anti-knock in petrol was responsible for their release in atmosphere.<\/li>\r\n \t
                        5. Nitrogen Oxides, NO<\/em>x<\/em> Due to high temperature inside internal combustion engine, N2 and O2 combine to form NOx<\/li>\r\n \t
                        6. Smoke\/Soot<\/em>. Particularly in diesel vehicles, the emission of the soot \/smoke is most visible. It is formed due to incomplete oxidation of carbon. The soot particles are polymeric substances having carbons chains (cyclic). The soot particle have free valance on surface and so these have great sticking property<\/li>\r\n \t
                        7. Particulates<\/em><\/li>\r\n \t
                        8. Odor. <\/em>This is due to partial oxidation of hydrocarbons into aldehydes. Petrol engines release larger amounts of CO (~3%) and unburnt HC. Diesel engines release more of NOX, smoke and odor.<\/li>\r\n<\/ol>\r\n \r\n\r\nMonitoring of Carbon Monoxide and Smoke<\/strong>\r\n

                          \u00a0 \u00a0Monitoring of CO is done through non -dispersive infrared (NDIR) method. Infrared radiation are generated through a hot filament, and then passed through a sample and a reference alternately.<\/p>\r\n \r\n

                          \u00a0 \u00a0Hatridge smoke meter, which is based on light extinction method, is used. The sample and reference are passed alternatively through a tube, at the one end of which is a light source and at the other end a photocell. The light reaching a photocell is converted into electric current, which is measured.<\/p>\r\nControl Measures.<\/strong>\r\n

                            \r\n \t
                          1. Proper maintenance of engine<\/li>\r\n \t
                          2. Petrol tank should be full. There are greater evaporative losses when the tank is only partially full.<\/li>\r\n \t
                          3. Use of catalytic converter in vehicles<\/li>\r\n<\/ol>\r\nRegional & Global Pollution<\/strong>\r\n

                            \u00a0 \u00a0The pollutants released at one location are known to be transported over large distances and sometimes without much dilution. Thus, the effects of pollution are both regional and global. The Arctic haze is caused by the transport of pollutants from northern Europe and Russia. An\u00a0 example\u00a0 of\u00a0 global\u00a0 effects\u00a0 of\u00a0 air\u00a0 pollution\u00a0 is\u00a0 the\u00a0 worldwide\u00a0 increase\u00a0 in\u00a0 the concentration of CO2, CH4, CFCs, N2O etc., which are responsible for global warming and climate change.<\/p>\r\n \r\n\r\nSevere Pollution Episodes<\/strong>\r\n

                            \u00a0 \u00a0Such episodes occur, when the rate of emission or formation of the pollutants exceeds the rate at which the pollutants are ventilated, destroyed or dispersed by winds or vertical transport or removed from the atmosphere by physical or chemical processes. London smog and Bhopal disaster are the examples of this type.<\/p>\r\n \r\n\r\nIndian Air Quality Standards<\/strong>\r\n

                            \u00a0 \u00a0Based on certain criteria, Central Pollution Control Board (Ministry of Environment & Forests, Govt. of India) has recommended the air quality standards to be followed by all in India. These are briefly described here. The control of air pollutants within a specified limit is necessary because of the following reasons:<\/p>\r\n\r\n

                              \r\n \t
                            1. Air pollution has caused many disasters, such as Bhopal Disaster, London smog, Los Angeles Smog, etc.<\/li>\r\n \t
                            2. Air pollution is known to affect human health badly.<\/li>\r\n \t
                            3. Air pollution toxicology studies require control of air pollutants.<\/li>\r\n \t
                            4. Pollutants are source of many kinds of adverse effects on humans, plants, animals and materials.<\/li>\r\n<\/ol>\r\nAir pollutants are responsible for climate change\/global warming, acid rain, smog, etc.\r\n\r\n \r\n\r\nBasis of Air Quality Regulations<\/strong>\r\n

                              \u00a0 \u00a0Easiest way of controlling air pollution is to close down all the factories, shut down all the thermal power plants, and ban the plying of all kinds of the automobiles. But this is not\u00a0 practical. It is, therefore, necessary that instead of stopping all developmental activities, focus must be on controlling the emission of each pollutant within n acceptable level. The Air Pollution Control Regulations have been made by Govt. of India and other countries. These regulations deal with emission, air quality and process.<\/p>\r\n \r\n\r\nComponents of Air Quality Standards<\/strong>\r\n

                              \u00a0 \u00a0The air quality standards define the acceptable level of each type of air pollutants without caring for its source. There are three components.<\/p>\r\n\r\n

                                \r\n \t
                              1. Identification of a pollutant and the method of its measurement.<\/li>\r\n \t
                              2. Selection of the averaging time, which is the period during which the concentration should not exceed a specified\u00a0\u00a0 value.\u00a0\u00a0\u00a0 It can be 1-h, 8-h, 24-h or annual.<\/li>\r\n \t
                              3. The level of an air pollutant in a numerical value that should not exceed.<\/li>\r\n<\/ol>\r\nObjectives of Indian Ambient Air Quality Standards<\/strong>\r\n\r\nAccording to CPCB, the objectives of air quality standards are:\r\n
                                  \r\n \t
                                1. To indicate the levels of air quality necessary with an adequate margin of safety to protect the public health, vegetation and property.<\/li>\r\n \t
                                2. To assist in establishing priorities for abatement and control of pollutant level.<\/li>\r\n \t
                                3. To provide uniform yardstick for assessing air quality at national level;<\/li>\r\n \t
                                4. To indicate the need and extent of monitoring program.<\/li>\r\n<\/ol>\r\n

                                  \u00a0 \u00a0CPCB has recommended the Indian standards for many pollutants. Some values are given in Table 1. The details can be found on the website of central Pollution Control Board, New Delhi.<\/p>\r\n\"\"\r\n\r\n\"\"\r\n\r\n\"\"\r\n\r\n\"\"\r\n\r\n\r\n\r\n
                                  you can view video on Air Pollution<\/strong><\/td>\r\n\"\"<\/a><\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
                                  \r\n

                                  References<\/strong><\/h3>\r\n
                                    \r\n \t
                                  1. H. A. Bridgeman (1990), Global Air Pollution: Problems for 1990s<\/em>. CBS Publishing Co., New Delhi.<\/li>\r\n \t
                                  2. D. J. Spedding (1974), Air Pollution<\/em>, Oxford University Press, London.<\/li>\r\n \t
                                  3. D.J. Jaccob (1999), Introduction to Atmospheric Chemistry,<\/em> Princeton University Press, Princeton.<\/li>\r\n \t
                                  4. J. H. seinfeld and S.N. PANDIS, (1998), Atmospheric Chemistry and Physics<\/em>: from Air<\/em> Pollution to Climate Change<\/em>, Wiley, New York.<\/li>\r\n \t
                                  5. J. Finlalyson-Pitts and J.N. Pitts, Jr. (1986), Atmospheric Chemistry: Fundamentals and<\/em> Experimental Techniques<\/em>, John Wiley, New York.<\/li>\r\n \t
                                  6. J. R. Barker (Ed.) (1995), Progress and Problems in Atmospheric Chemistry<\/em>, World Scientific, Singapore.<\/li>\r\n \t
                                  7. R.P. Wayne (2000), Chemistry of Atmospheres ,<\/em> Oxford University Press, Oxford.<\/li>\r\n \t
                                  8. P.V. HOBBS, (2000), Introduction to Atmospheric Chemistry,<\/em> Cambridge University Press, Cambridge<\/li>\r\n \t
                                  9. Global Climate Change<\/em>, Department of Environment, London(1991).<\/li>\r\n \t
                                  10. P. Brimblecombe (1996) Air Composition and Chemistry,<\/em> Cambridge University Press, Cambridge.<\/li>\r\n \t
                                  11. Colin Baird (1998), Environmental Chemistry,<\/em> W.H. Freeman, New York.<\/li>\r\n \t
                                  12. R. F. Phelan and R. N. Phelan(2013), Introduction to Air Pollution Chemistry- A Public Health<\/em> Perspective<\/em>, Jones and Bartlett, Burlington, MA.<\/li>\r\n \t
                                  13. J. Gerard(2012), Introduction to Environmental Chemistry<\/em>, Jones and Bartlett, New Delhi<\/li>\r\n \t
                                  14. Guidelines for the Measurement of Ambient Air Pollutants, Volume-I(2011),<\/strong> Central Pollution Control Board (Ministry of Environment & Forests, Govt. of India)<\/li>\r\n<\/ol>\r\n

                                    Website: http:\/\/www.cpcb.nic.in<\/p>\r\n \r\n\r\n<\/div>","rendered":"

                                    \"epgp<\/a>
                                    \n<\/span><\/div>\n

                                     <\/p>\n

                                     <\/p>\n

                                    Contents<\/strong><\/p>\n

                                      \n
                                    1. What is Air Pollution?<\/li>\n
                                    2. Classification of Pollutants<\/li>\n
                                    3. Sources of Pollutants<\/li>\n
                                    4. Criteria Air Contaminants(CAC) or Criteria Pollutants<\/li>\n
                                    5. Processes Responsible for Air Pollutants<\/li>\n
                                    6. Sources of Sulfur Dioxide<\/li>\n
                                    7. Natural Sources<\/li>\n
                                    8. Anthropogenic Sources<\/li>\n
                                    9. Control of Carbon Monoxide Pollution<\/li>\n
                                    10. Urban Air Pollution<\/li>\n
                                    11. Monitoring of Carbon Monoxide and Smoke<\/li>\n
                                    12. Regional & Global Pollution<\/li>\n
                                    13. Indian Air Quality Standards<\/li>\n
                                    14. Basis of Air Quality Regulations<\/li>\n
                                    15. Components of Air Quality Standards<\/li>\n
                                    16. Objectives of Indian Ambient Air Quality Standards<\/li>\n
                                    17. References<\/li>\n<\/ol>\n

                                      What is Air Pollution?<\/strong><\/p>\n

                                      Air pollution occurs, when harmful and toxic gases, dust and smoke, etc, enter the atmosphere.<\/p>\n

                                       <\/p>\n

                                      \u00a0 \u00a0These make the survival of humans, plants and animals difficult and also disfigure the buildings and lead to deterioration of assets.According to Brimblecombe (1996), air pollution occurs when the substances are released into the air by human activities in such concentrations as are sufficient to cause detrimental effect on human health, vegetation, animals and property or interfere with the enjoyment of the property by the mankind. So the contamination of air whether inside or outside the house is the cause of air pollution. These cause physical, biological or chemical changes in air, which if harmful, cause air pollution. The composition of air is given in Table 1<\/p>\n

                                       <\/p>\n

                                      Table 1. <\/strong>Composition of dry unpolluted air (Brimblecombe, 1996, Girard, 2011).<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
                                      Gases<\/strong><\/td>\nPer cent<\/strong><\/td>\n<\/tr>\n
                                      Nitrogen<\/strong><\/td>\n78.084%<\/strong><\/td>\n<\/tr>\n
                                      Oxygen<\/strong><\/td>\n20.946%<\/strong><\/td>\n<\/tr>\n
                                      Argon<\/strong><\/td>\n0.934$%<\/strong><\/td>\n<\/tr>\n
                                      Carbon dioxide<\/strong><\/td>\n0.039%<\/strong><\/td>\n<\/tr>\n
                                      Neon<\/strong><\/td>\n0.0018%<\/strong><\/td>\n<\/tr>\n
                                      Helium<\/strong><\/td>\n0.000526%<\/strong><\/td>\n<\/tr>\n
                                      Methane<\/strong><\/td>\n0.00016%<\/strong><\/td>\n<\/tr>\n
                                      Krypton<\/strong><\/td>\n0.00005%<\/strong><\/td>\n<\/tr>\n
                                      Hydrogen<\/strong><\/td>\n0.00003%<\/strong><\/td>\n<\/tr>\n
                                      Nitrous oxide<\/strong><\/td>\n0.00003%<\/strong><\/td>\n<\/tr>\n
                                      Ozone<\/strong><\/td>\nTrace to 0.0008%<\/strong><\/td>\n<\/tr>\n
                                      Carbon monoxide<\/strong><\/td>\nTrace to 0.000025<\/strong><\/td>\n<\/tr>\n
                                      Sulfur dioxide<\/strong><\/td>\nTrace to 0.00001%<\/strong><\/td>\n<\/tr>\n
                                      Nitrogen dioxide<\/strong><\/td>\nTrace to 0.000002%<\/strong><\/td>\n<\/tr>\n
                                      Ammonia<\/strong><\/td>\nTrace to 0.0000003%<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

                                       <\/p>\n

                                      \u00a0 \u00a0It is remarkable to note that the concentration of pollutant gases is less than 0.1% but their toxic effects are highest. Out of the list in Table 1, the pollutant gases are tropospheric ozone, nitrogen oxides, sulfur dioxide, carbon monoxide, ammonia, methane, etc.<\/p>\n

                                       <\/p>\n

                                      Classification of Pollutants<\/strong><\/p>\n

                                      The pollutants can be classified in distinct groups in a variety of ways, some of which are follows.<\/p>\n

                                       <\/p>\n

                                        \n
                                      1. Primary Pollutants<\/strong><\/li>\n<\/ol>\n

                                        These are released directly into the air from the source. Based on physical state<\/strong>, these are classified as follows.<\/p>\n

                                        (i) Gaseous Primary Pollutants<\/em><\/strong><\/p>\n

                                        Some of the gaseous pollutants are as follows.<\/p>\n

                                        (a) Sulfur dioxide, SO2<\/p>\n

                                        (b) Nitrogen oxides, NOx<\/em>. ( NOx = NO + NO2<\/span><\/p>\n

                                        (c) Hydrocarbons(CH4, propane, ethylene, etc); volatile organic compounds(VOCs); polycyclic aromatic hydrocarbons(PAHs), and large number of other organic compound<\/p>\n

                                        (d) Carbon monoxide, CO<\/p>\n

                                        (e) Tropospheric ozone, O3<\/p>\n

                                        (f) Carbon dioxide, CO2, chlorofluorocarbons (CFCs), halons, nitrous oxide, N2 Although these pollutants as such do not have any detrimental effect but are implicated in global climate change.<\/p>\n

                                         <\/p>\n

                                        (ii) Primary Aerosols<\/strong><\/p>\n

                                        \u00a0 \u00a0Aerosols are dispersions of solid \/liquid particulates in air. The primary particulates like soil particles, fly ash , smoke etc. are directly released in air<\/p>\n

                                         <\/p>\n

                                        Depending on the source\/origin air pollutants are classified as<\/strong><\/p>\n

                                          \n
                                        1. a) Primary air pollutants and b) Secondary air pollutants<\/em><\/li>\n<\/ol>\n

                                           <\/p>\n

                                            \n
                                          1. a) <\/strong>Primary air pollutants<\/strong><\/li>\n<\/ol>\n

                                            \u00a0 \u00a0Primary air pollutants are those that are emitted directly from the identifiable sources. The examples of primary air pollutants:<\/p>\n

                                            \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 i) Carbon monoxide<\/p>\n

                                            \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0ii) NOx ( oxides of nitrogen<\/p>\n

                                            \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 iii) SOx ( oxides of sulphur)<\/p>\n

                                            \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 iv) Hydrocarbons<\/p>\n

                                            \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 v) Particulate matter<\/p>\n

                                              \n
                                            1. b) Secondary air Pollutants<\/strong><\/li>\n<\/ol>\n

                                              \u00a0 \u00a0The pollutants that are produced by the interaction among two or more primary air pollutants in the air or by reaction with constituents of air. These pollutants are formed in air due to the photochemical and thermal reactions of primary pollutants. For example, aerosols, ground level ozone, peroxyacetyl nitrate (PAN), tropospheric ozone, acid rain, photochemical smog are the pollutants of this type.<\/p>\n

                                               <\/p>\n

                                              \u00a0 \u00a0 \u00a0 \u00a0(i)\u00a0 Secondary Gaseous Pollutants<\/em><\/strong><\/p>\n

                                              \u00a0 \u00a0These are generated in air through chemical reactions. Some of these are as follows:<\/p>\n

                                                \n
                                              1. Tropospheric ozone, O3.<\/li>\n
                                              2. Aldehydes.<\/li>\n
                                              3. Peroxyacetylnitrate etc.<\/li>\n<\/ol>\n

                                                \u00a0 \u00a0 \u00a0 \u00a0 \u00a0(ii) <\/em><\/strong>Secondary Aerosols<\/em><\/strong><\/p>\n

                                                \u00a0 \u00a0These are formed in air, mostly through gas to particulate conversion, e.g., SO2 to sulfate aerosol, NOx to nitrate aerosols, ammonia into ammonium sulfate aerosol, VOCs into carbonaceous particles etc.<\/p>\n

                                                 <\/p>\n

                                                Source \u2013 Dependent Classification of Aerosols<\/strong><\/p>\n

                                                Based on the origin of aerosols, these are classified as follows.<\/p>\n

                                                 <\/p>\n

                                                \u00a0 (i) <\/em>Biological Aerosols<\/em><\/strong><\/p>\n

                                                These\u00a0 are\u00a0 of\u00a0 biological\u00a0 origin,\u00a0 viz.,\u00a0 seeds,\u00a0 pollens,\u00a0 spores,\u00a0 fragments\u00a0 of\u00a0 plants\/ animals\/insects, hair, bacteria, fungi, micro-organisms, algae, protozoa, viruses etc.<\/p>\n

                                                (ii) Geochemical Aerosols<\/em><\/strong><\/p>\n

                                                These aerosols are made up of geo-chemicals and are directly injected into air due to volcanic eruptions, mining, crushing, blasting, dispersion of dust through wind or human activities.<\/p>\n

                                                (iii) Oceanic Aerosols<\/em><\/strong><\/p>\n

                                                (iv) Anthropogenic Aerosols<\/em><\/strong><\/p>\n

                                                Fossil fuel combustion, biomass burning, industrial activities, e.g., manufacturing and metallurgical processes , cement plants etc. are some of the big sources. Automobiles are other big sources of this type of aerosols.<\/p>\n

                                                (v) <\/strong>Other Sources of Aerosols<\/em><\/strong><\/p>\n

                                                Some other sources of aerosols are forest fires and meteoritic debris.<\/p>\n

                                                 <\/p>\n

                                                Chemical Composition \u2013 Based Classification of Aerosols<\/em><\/strong><\/p>\n

                                                Based on chemical composition the aerosols are classified as follows.<\/p>\n

                                                 <\/p>\n

                                                (i) Inorganic Aerosols<\/em><\/strong><\/p>\n

                                                Basically, these are made from inorganic compounds and further divided in two categories<\/p>\n

                                                \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0Soluble Aerosols<\/strong>: These are soluble in water. The aerosols of salts like NaCl, and (NH4)2SO4 are of this type.<\/p>\n

                                                \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0Insoluble Aerosols<\/strong>: The examples of aerosols this type include those derived from minerals, stones, etc. These are not soluble in water.<\/p>\n

                                                 <\/p>\n

                                                (ii) Organic Aerosols<\/em><\/strong><\/p>\n

                                                These are made from organic compounds. Examples are carbonaceous particles, polycyclic hydrocarbons(PAHs), soot, etc<\/p>\n

                                                 <\/p>\n

                                                Sources of Pollutants<\/strong><\/p>\n

                                                There are innumerable sources of air pollutants, some known and some unknown. According to Phalen and Phalen (2013), these sources can classified in many ways as mentioned below<\/p>\n

                                                 <\/p>\n

                                                (i) Natural Sources: <\/strong>The natural processes such as volcanoes, lightning, storms, etc, fall\u00a0 in this category.<\/p>\n

                                                (ii) Anthropogenic Sources<\/strong>: Human activities constitute manmade or anthropogenic<\/p>\n

                                                (iii) Secondary Sources<\/strong>: The processes of formation of pollutants in atmosphere due to reactions of natural and manmade pollutants are secondary sources.<\/p>\n

                                                 <\/p>\n

                                                Pollutant sources have been categorized in following manner also.<\/p>\n

                                                (i) Stationary Sources<\/strong>: Such as homes, factories, power plants, etc.<\/p>\n

                                                (ii) Mobile Sources<\/strong>: Such as vehicles, trains, aircrafts, ships, tractors, etc.<\/p>\n

                                                 <\/p>\n

                                                A further subdivision of pollutants as given below has also been proposed.<\/p>\n

                                                 <\/p>\n

                                                (i) Indoor Pollutant Sources<\/strong>: Such as kitchen<\/p>\n

                                                (ii) Outdoor Pollutant Sources:<\/strong> The sources outside the homes<\/p>\n

                                                (iii) Point Sources:<\/strong> Highly localized such as power plants, factories.<\/p>\n

                                                (iv) Distributed Sources<\/strong>: Such as agricultural operations and cities<\/p>\n

                                                (v) Local Sources:<\/strong> such as power plants<\/p>\n

                                                (vi) Global Sources<\/strong>, Dust, soil, biological processes, volcanoes<\/p>\n

                                                (vii) Inorganic Sources<\/strong>. Soil, etc.<\/p>\n

                                                (viii) Organic Sources,<\/strong> Agricultural processes, etc.<\/p>\n

                                                 <\/p>\n

                                                Criteria Air Contaminants (CAC) or Criteria Pollutants<\/strong><\/p>\n

                                                \u00a0 \u00a0A set of six most common air pollutants, viz., carbon monoxide, nitrogen dioxide, lead, ozone, sulfur dioxide and particulate matter selected by US Environmental Agency that cause smog, acid rain and other health hazards, are called criteria air contaminants. These are generally emitted by sources in industry, transportation, mining, electric generation, agriculture. Mostly these are produced by combustion of fossil fuels or industrial processes. These substances have defined allowable concentrations in ambient air as per national air quality standard. This national quality standard has to be revised every five year. These contaminants are considered to present a general risk to the health of the public.<\/p>\n

                                                 <\/p>\n

                                                Hazardous Pollutants<\/strong><\/p>\n

                                                \u00a0 \u00a0US EPA has another list of about 200 substances, which are believed to cause adverse health or environmental effects. This list includes compounds such as benzene, asbestos, arsenic and nickel compounds, formaldehyde, radionuclides etc. This list can undergo change at any time.<\/p>\n

                                                 <\/p>\n

                                                Processes Responsible for Air Pollutants<\/strong><\/p>\n

                                                \u00a0 \u00a0Brimblecombe (1996) has categorized the anthropogenic processes responsible for the formation and release of pollutants in atmosphere as follows.<\/p>\n

                                                  \n
                                                1. Combustion of Fuels:\u00a0\u00a0<\/strong>Combustion of fossil fuels, such as coal, petroleum products, hydrocarbons, etc. is the most significant source of pollutants. The pollutants released are CO2 – major culprit of global warming, carbon monoxide, sulfur dioxide, unburnt hydrocarbons, nitrogen oxides, polycyclic aromatic hydrocarbons(PAHs), etc. The toxic metals in different chemical forms are also released.<\/li>\n<\/ol>\n
                                                    \n
                                                  1. Incineration:\u00a0<\/strong>\u00a0 Incineration of municipal waste, which contains chlorine compounds, such as polyvinylchloride, present as impurity is a source of HCl, CH3Cl, etc. Possibly, it is a source of several highly toxic and carcinogenic chlorinated dioxins and furans.<\/li>\n<\/ol>\n
                                                      \n
                                                    1. High Temperature Sources:\u00a0\u00a0<\/strong>The metallurgical processes such as smelting and brick making are high temperature sources, which release pollutants such as carbon dioxide( manufacture of cement), sulfur dioxide(smelting of sulfide ores), toxic metals like arsenic(present as impurity), hydrogen fluoride( brick making and cryolite smelting for production of aluminum), etc.<\/li>\n<\/ol>\n
                                                        \n
                                                      1. Evaporation of Volatile Organic Compounds(VOCs):\u00a0\u00a0<\/strong>It is considered a low temperature source. The evaporation of VOCs takes place from solvent use, petroleum industries, etc. Mining and gas leakage are other sources. The use of pesticides in agriculture is a worrisome source of toxic organic compounds. In the next section, the sources of individual pollutants in somewhat detail are discussed.<\/li>\n<\/ol>\n

                                                         <\/p>\n

                                                        Sources of Sulfur Dioxide<\/strong><\/p>\n

                                                        Natural Sources<\/em><\/strong><\/p>\n

                                                        \u00a0 Volcanoes and oxidation of sulfur gases produced by decomposition of plants are the important natural sources of sulfur dioxide. Other sources are sulfur- based hot springs and geysers. Since the natural sulfur dioxide by volcanoes is released high in the atmosphere, and by other sources at far from the populated areas, its background concentration remains low (about 1 ppb).<\/p>\n

                                                         <\/p>\n

                                                        Anthropogenic Sources<\/em><\/strong><\/p>\n

                                                        (i) <\/strong>Coal Combustion<\/em><\/strong><\/p>\n

                                                        \u00a0 \u00a0Coal combustion is the biggest manmade source of atmospheric SO2. Depending upon the area from which coal is mined, it contains 1-9% sulfur. This sulfur is present in two forms. About half of the sulfur is present as inclusions in the mineral content of the coal. By pulverizing the coal before combustion, this sulfur can be removed mechanically. The remaining sulfur is a part of coal matrix and is bonded in the complex coal structure. Removal of this sulfur requires complex and costly processing.<\/p>\n

                                                         <\/p>\n

                                                        (ii) Petroleum<\/em><\/strong><\/p>\n

                                                        \u00a0 \u00a0Crude oil contains few percent of sulfur. However, during refining it is reduced to few ppm in gasoline. Refining is responsible for the release of some SO2 in the atmosphere.<\/p>\n

                                                         <\/p>\n

                                                        (iv)Natural Gas<\/em><\/strong><\/p>\n

                                                        \u00a0 \u00a0Natural gas also contains sulfur compounds, mainly H2S. The cleaning of natural gas is responsible for the release of some H2S.<\/p>\n

                                                         <\/p>\n

                                                        (iii) Smelting<\/strong><\/p>\n

                                                        \u00a0 \u00a0Many metals such as nickel and copper occur in nature in the form of sulfide ores. When these ores are roasted, sulfur is oxidized and SO2 is formed. The sulfur dioxide so formed may be\u00a0\u00a0\u00a0 obtained in the liquefied form or converted to H2SO4.<\/p>\n

                                                         <\/p>\n

                                                        (iv) Paper and Pulp Manufacture<\/strong><\/p>\n

                                                        \u00a0 \u00a0Wood pulping uses hot sulfite is used in wood pulping and so the process releases some SO2. Is H2S, which on oxidation forms SO2, is released by kraft pulping process.<\/p>\n

                                                         <\/p>\n

                                                        Sources of Carbon Monoxide<\/strong><\/p>\n

                                                        \u00a0 \u00a0CO is a tasteless and odorless gas. Because of latter property, one is unable to feel\/<\/strong>recognize its inhalation, which may result in death.<\/p>\n

                                                         <\/p>\n

                                                        Natural Sources<\/strong><\/p>\n

                                                        \u00a0 \u00a0The natural sources are oxidation of methane, terpenes, isoprene, forest fires, lightning, seed germination, etc. Its background concentration is ~ 100 ppb and it is the most abundant criteria air contaminant(CAC).<\/p>\n

                                                         <\/p>\n

                                                        Anthropogenic Sources<\/strong><\/p>\n

                                                        \u00a0 \u00a0The major manmade sources are industrial units and automobiles which produce CO due to incomplete combustion of carbon containing fuels. Complete oxidation of carbon produces CO2. The incomplete combustion due to insufficient oxygen is responsible for some partial oxidation of carbon.<\/p>\n

                                                        \"\"\u00a0 \u00a0In carbon containing high temperature processes, such as smelting of iron in blast furnace, carbon reacts with CO2 to produce large amount of CO.<\/p>\n

                                                        \"\"\u00a0 \u00a0The incomplete combustion of hydrocarbon fuels in automobiles is the most significant source of CO pollution in urban areas. For pure octane the correct air to fuel(AFR) ratio is 14.7. Actually this ratio depends upon the composition of fuel, which is a mixture of several hydrocarbons and may have some oxygenate organic compounds also. If the mixture is rich (more fuel), there is insufficient oxygen to completely oxidize carbon into CO2, resulting in the formation and emission of CO. On the other hand if the AFR is higher than stoichiometric amount, the mixture is considered lean. Lean mixtures are more efficient in ensuring nearly complete oxidation of carbon into CO2 but produce higher levels of nitrogen oxides.<\/p>\n

                                                         <\/p>\n

                                                        Control of Carbon Monoxide Pollution<\/strong><\/p>\n

                                                        \u00a0 \u00a0The automobiles are the sources of many notorious pollutants. Therefore, the techniques to control CO formation in internal combustion engine, and to convert CO formed in to CO2 before release are employed. The use of three-way catalytic converters in automobiles is now mandatory to control the air pollution. It is so named because it simultaneously reduce the amounts of CO, hydrocarbons and NOx. It consists of a ceramic honeycomb, impregnated with catalysts platinum, palladium and rhodium. It has two chambers. Engine gases containing CO, NOx and HC enter the chamber. At the surface of the catalyst, reaction of hydrocarbons(HC) with water produces H2. Rhodium catalyzes the reduction of NO by H2.<\/p>\n

                                                         <\/p>\n

                                                        \"\"\u00a0 \u00a0Then excess air is pumped into exhaust stream to make available oxygen, which on catalysis by Pt and Pd, oxidizes CO in to CO2 and HC into CO2 and H2O.<\/p>\n

                                                        \u00a0 \u00a0The major natural sink of CO in atmosphere is the oxidation of CO by OH radicals into CO2. Soil microorganisms also remove CO.<\/p>\n

                                                         <\/p>\n

                                                        Ground Level Ozone<\/strong><\/p>\n

                                                        The major source of ozone is photochemical reactions in troposphere as discussed in a subsequent module.<\/p>\n

                                                         <\/p>\n

                                                        Volatile Organic Compounds\/Hydrocarbons<\/strong><\/p>\n

                                                        The detailed atmospheric chemistry including sources are presented in a separate Module on VOC.<\/p>\n

                                                         <\/p>\n

                                                        Urban Air Pollution<\/strong><\/p>\n

                                                        \u00a0 \u00a0There has been a massive growth in the size and the population of the cities, in particular, in developing countries. An endless stream of automobiles is being added each year. This has led to deterioration in the quality of air in the cities and neighboring areas. The air pollution has increased. The urban air pollution is an important factor in changing the climate of cities.<\/p>\n

                                                         <\/p>\n

                                                        The following urban characteristics seriously affect the urban climate.<\/p>\n

                                                          \n
                                                        1. Creation of urban heat islands<\/li>\n
                                                        2. Lower average wind speeds<\/li>\n
                                                        3. Increase in fog frequency<\/li>\n
                                                        4. Changes in the vertical structure of the lower boundary layer<\/li>\n
                                                        5. Formation of meso-scale circulation systems, etc<\/li>\n<\/ol>\n

                                                          \u00a0 \u00a0The major pollution factors, which are briefly discussed below, are waste heat, sulfur dioxide, carbon monoxide, nitrogen oxides, hydrocarbons\/organic compounds, photochemical oxidants and suspended particulate matter.<\/p>\n

                                                           <\/p>\n

                                                          Waste Heat<\/strong><\/p>\n

                                                          \u00a0 \u00a0Waste heat is an important aspect of urban temperature and moisture content. It is unique to urban environments due to dense network of sources of heat. It is likely to aid in the formation of secondary pollutants.<\/p>\n

                                                           <\/p>\n

                                                          Sources of waste heat<\/em><\/strong><\/p>\n

                                                          Automobiles and transportation exhausts<\/p>\n

                                                          Industrial emissions<\/p>\n

                                                          Power plant plumes.<\/p>\n

                                                          Domestic heating\/<\/strong>cooking<\/p>\n

                                                          Air conditioning<\/p>\n

                                                           <\/p>\n

                                                          Excess heat stored in buildings, pavements, roads and other structures which heat up fast<\/p>\n

                                                          \u00a0 \u00a0In urban centers due to lack of plant cover only small fraction of this heat is used for evapo-transpiration. Most of the heat is released as sensible heat and small portion as infrared radiation and latent heat. In India waste heat influence is most noticeable in summers.<\/p>\n

                                                           <\/p>\n

                                                          \u00a0 \u00a0The waste heat flux is determined largely by density of sources. The average heat released by cities shows the large spatial variation. For example, the annual heat released by Manhattan city has been reported to be about 17.4 GW (in summer) and 21.8 (in winter). The heat fluxes varied widely from 5 W\/m2 on the urban fringes to >100 W\/m2 in the city centre. These values are large when compared with annual average net radiation balance at earth surface in mid – latitude of about 100 W\/m2. Thus, the cities add a significant portion of artificial heat to radiation balance.<\/p>\n

                                                          Obviously, the temperature in the city is likely to be higher than the surrounding areas.<\/p>\n

                                                          However, the total contribution of cities to earth radiation balance on global scale is negligible.<\/p>\n

                                                          Nevertheless, at the local scale this is serious.<\/p>\n

                                                           <\/p>\n

                                                          Automobile Exhaust Emissions<\/em><\/strong><\/p>\n

                                                          The major pollutants released by automobile exhaust are as follows.<\/p>\n

                                                            \n
                                                          1. Carbon monoxide, CO. <\/em>It is the most abundant pollutant in urban areas. It is formed due to incomplete combustion of carbonaceous fuels. The correct air to fuel ratio is ~ 14.5. If the mixture is rich (more fuel), there is insufficient oxygen to completely oxidize carbon into CO2 resulting in the formation and emission of CO.<\/li>\n
                                                          2. Unburnt hydrocarbons. <\/em>In urban areas the exhaust emissions, evaporative losses from fuel tank, carburetor etc. are the major sources of polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs). Many of these are highly toxic and carcinogenic. Ethylene is produced in petrol engines due to use of ethylene dibromide and dichloride.<\/li>\n
                                                          3. Sulfur Dioxide, SO<\/em>2<\/em> .This is formed due to oxidation of sulfur present in fuel.<\/li>\n
                                                          4. Organic \/ Inorganic Lead \u2013 Compounds. <\/em>Use of tetraethyllead(TEL)( now banned) as anti-knock in petrol was responsible for their release in atmosphere.<\/li>\n
                                                          5. Nitrogen Oxides, NO<\/em>x<\/em> Due to high temperature inside internal combustion engine, N2 and O2 combine to form NOx<\/li>\n
                                                          6. Smoke\/Soot<\/em>. Particularly in diesel vehicles, the emission of the soot \/smoke is most visible. It is formed due to incomplete oxidation of carbon. The soot particles are polymeric substances having carbons chains (cyclic). The soot particle have free valance on surface and so these have great sticking property<\/li>\n
                                                          7. Particulates<\/em><\/li>\n
                                                          8. Odor. <\/em>This is due to partial oxidation of hydrocarbons into aldehydes. Petrol engines release larger amounts of CO (~3%) and unburnt HC. Diesel engines release more of NOX, smoke and odor.<\/li>\n<\/ol>\n

                                                             <\/p>\n

                                                            Monitoring of Carbon Monoxide and Smoke<\/strong><\/p>\n

                                                            \u00a0 \u00a0Monitoring of CO is done through non -dispersive infrared (NDIR) method. Infrared radiation are generated through a hot filament, and then passed through a sample and a reference alternately.<\/p>\n

                                                             <\/p>\n

                                                            \u00a0 \u00a0Hatridge smoke meter, which is based on light extinction method, is used. The sample and reference are passed alternatively through a tube, at the one end of which is a light source and at the other end a photocell. The light reaching a photocell is converted into electric current, which is measured.<\/p>\n

                                                            Control Measures.<\/strong><\/p>\n

                                                              \n
                                                            1. Proper maintenance of engine<\/li>\n
                                                            2. Petrol tank should be full. There are greater evaporative losses when the tank is only partially full.<\/li>\n
                                                            3. Use of catalytic converter in vehicles<\/li>\n<\/ol>\n

                                                              Regional & Global Pollution<\/strong><\/p>\n

                                                              \u00a0 \u00a0The pollutants released at one location are known to be transported over large distances and sometimes without much dilution. Thus, the effects of pollution are both regional and global. The Arctic haze is caused by the transport of pollutants from northern Europe and Russia. An\u00a0 example\u00a0 of\u00a0 global\u00a0 effects\u00a0 of\u00a0 air\u00a0 pollution\u00a0 is\u00a0 the\u00a0 worldwide\u00a0 increase\u00a0 in\u00a0 the concentration of CO2, CH4, CFCs, N2O etc., which are responsible for global warming and climate change.<\/p>\n

                                                               <\/p>\n

                                                              Severe Pollution Episodes<\/strong><\/p>\n

                                                              \u00a0 \u00a0Such episodes occur, when the rate of emission or formation of the pollutants exceeds the rate at which the pollutants are ventilated, destroyed or dispersed by winds or vertical transport or removed from the atmosphere by physical or chemical processes. London smog and Bhopal disaster are the examples of this type.<\/p>\n

                                                               <\/p>\n

                                                              Indian Air Quality Standards<\/strong><\/p>\n

                                                              \u00a0 \u00a0Based on certain criteria, Central Pollution Control Board (Ministry of Environment & Forests, Govt. of India) has recommended the air quality standards to be followed by all in India. These are briefly described here. The control of air pollutants within a specified limit is necessary because of the following reasons:<\/p>\n

                                                                \n
                                                              1. Air pollution has caused many disasters, such as Bhopal Disaster, London smog, Los Angeles Smog, etc.<\/li>\n
                                                              2. Air pollution is known to affect human health badly.<\/li>\n
                                                              3. Air pollution toxicology studies require control of air pollutants.<\/li>\n
                                                              4. Pollutants are source of many kinds of adverse effects on humans, plants, animals and materials.<\/li>\n<\/ol>\n

                                                                Air pollutants are responsible for climate change\/global warming, acid rain, smog, etc.<\/p>\n

                                                                 <\/p>\n

                                                                Basis of Air Quality Regulations<\/strong><\/p>\n

                                                                \u00a0 \u00a0Easiest way of controlling air pollution is to close down all the factories, shut down all the thermal power plants, and ban the plying of all kinds of the automobiles. But this is not\u00a0 practical. It is, therefore, necessary that instead of stopping all developmental activities, focus must be on controlling the emission of each pollutant within n acceptable level. The Air Pollution Control Regulations have been made by Govt. of India and other countries. These regulations deal with emission, air quality and process.<\/p>\n

                                                                 <\/p>\n

                                                                Components of Air Quality Standards<\/strong><\/p>\n

                                                                \u00a0 \u00a0The air quality standards define the acceptable level of each type of air pollutants without caring for its source. There are three components.<\/p>\n

                                                                  \n
                                                                1. Identification of a pollutant and the method of its measurement.<\/li>\n
                                                                2. Selection of the averaging time, which is the period during which the concentration should not exceed a specified\u00a0\u00a0 value.\u00a0\u00a0\u00a0 It can be 1-h, 8-h, 24-h or annual.<\/li>\n
                                                                3. The level of an air pollutant in a numerical value that should not exceed.<\/li>\n<\/ol>\n

                                                                  Objectives of Indian Ambient Air Quality Standards<\/strong><\/p>\n

                                                                  According to CPCB, the objectives of air quality standards are:<\/p>\n

                                                                    \n
                                                                  1. To indicate the levels of air quality necessary with an adequate margin of safety to protect the public health, vegetation and property.<\/li>\n
                                                                  2. To assist in establishing priorities for abatement and control of pollutant level.<\/li>\n
                                                                  3. To provide uniform yardstick for assessing air quality at national level;<\/li>\n
                                                                  4. To indicate the need and extent of monitoring program.<\/li>\n<\/ol>\n

                                                                    \u00a0 \u00a0CPCB has recommended the Indian standards for many pollutants. Some values are given in Table 1. The details can be found on the website of central Pollution Control Board, New Delhi.<\/p>\n

                                                                    \"\"<\/p>\n

                                                                    \"\"<\/p>\n

                                                                    \"\"<\/p>\n

                                                                    \"\"<\/p>\n\n\n\n
                                                                    you can view video on Air Pollution<\/strong><\/td>\n\"\"<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
                                                                    \n

                                                                    References<\/strong><\/h3>\n
                                                                      \n
                                                                    1. H. A. Bridgeman (1990), Global Air Pollution: Problems for 1990s<\/em>. CBS Publishing Co., New Delhi.<\/li>\n
                                                                    2. D. J. Spedding (1974), Air Pollution<\/em>, Oxford University Press, London.<\/li>\n
                                                                    3. D.J. Jaccob (1999), Introduction to Atmospheric Chemistry,<\/em> Princeton University Press, Princeton.<\/li>\n
                                                                    4. J. H. seinfeld and S.N. PANDIS, (1998), Atmospheric Chemistry and Physics<\/em>: from Air<\/em> Pollution to Climate Change<\/em>, Wiley, New York.<\/li>\n
                                                                    5. J. Finlalyson-Pitts and J.N. Pitts, Jr. (1986), Atmospheric Chemistry: Fundamentals and<\/em> Experimental Techniques<\/em>, John Wiley, New York.<\/li>\n
                                                                    6. J. R. Barker (Ed.) (1995), Progress and Problems in Atmospheric Chemistry<\/em>, World Scientific, Singapore.<\/li>\n
                                                                    7. R.P. Wayne (2000), Chemistry of Atmospheres ,<\/em> Oxford University Press, Oxford.<\/li>\n
                                                                    8. P.V. HOBBS, (2000), Introduction to Atmospheric Chemistry,<\/em> Cambridge University Press, Cambridge<\/li>\n
                                                                    9. Global Climate Change<\/em>, Department of Environment, London(1991).<\/li>\n
                                                                    10. P. Brimblecombe (1996) Air Composition and Chemistry,<\/em> Cambridge University Press, Cambridge.<\/li>\n
                                                                    11. Colin Baird (1998), Environmental Chemistry,<\/em> W.H. Freeman, New York.<\/li>\n
                                                                    12. R. F. Phelan and R. N. Phelan(2013), Introduction to Air Pollution Chemistry- A Public Health<\/em> Perspective<\/em>, Jones and Bartlett, Burlington, MA.<\/li>\n
                                                                    13. J. Gerard(2012), Introduction to Environmental Chemistry<\/em>, Jones and Bartlett, New Delhi<\/li>\n
                                                                    14. Guidelines for the Measurement of Ambient Air Pollutants, Volume-I(2011),<\/strong> Central Pollution Control Board (Ministry of Environment & Forests, Govt. of India)<\/li>\n<\/ol>\n

                                                                      Website: http:\/\/www.cpcb.nic.in<\/p>\n

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