The immediate environment of mancomprises of air on which depends all forms of life.The atmosphere is a complex, dynamic natural gaseous system, essential to support life on planet Earth.
Air is a mechanical mixture of gases.The normal composition is approximately as follows: - Nitrogen-78%, - Oxygen-21%, - Carbon dioxide-0.03%and other gases – argon, neon, helium, as wellas water vapor and suspended matter such as dust, bacteria, spores.
Apart from supplying the life-giving oxygen,air and atmospheric conditions serve several functions:The human body is cooled by the air contact; the senses of hearing and smell function through air-transmitted stimuli; disease agents may be conveyed by air. Pollution of air by dust, smoke, toxic gasesand chemical vapors could result in sickness and death.
The phenomenon called “pollution” is an inescapableconsequence of the presence of man and hisactivities.The term “air pollution” signifies the presence in thesurrounding atmosphere of chemicals, particulatematter, or biological materials generated by theactivities of man in high enough concentrations thatcause harm or discomfort to humans or other livingorganisms, or damages the natural environment,resulting in chemical entering the food chain orbeing present in drinking-water and constitutingadditional source of human exposure.
Air pollution is one of the present-day healthproblems throughout the world. Abundant amounts of air pollution changesnatural atmospheric processes, causing acid rains,ozone hole, and enhancing greenhouse effect.Additionally, it causes economic losses. The direct effect of air pollutants on plants,animals and soil can influence the structure and functionof ecosystems, including self-regulation ability, therebyaffecting the quality of life.
An air pollutant is a substance in the air that cancause harm to humans and the environment.Pollutants can be in the form of:- solid particles,- liquid droplets,- gases.In addition, they may be natural or man-made.Examples of natural sources of air pollution includeforest fires, pollen, volcanic emissions, and dust.Human sources of air pollutants include emissionsfrom industry, agriculture, forestry, transportation,power generation, and space heating.
Pollutants are classified either asprimary pollutants, or those that enter theatmosphere directly from various sources, or as secondary pollutants, or those that areformed when primary pollutants react witheach other or with other compounds present in the atmosphere.
Usually, primary pollutants are substances directly emitted from a process, such as ash from a volcanic eruption, the carbon monoxide gas from a motor vehicle exhaust or sulfur dioxide released from factories.Secondary pollutants are not emitted directly. Rather,they form in the air when primary pollutants react or interact. An important example of a secondary pollutant is ground level ozone - one of the many secondary pollutants that make up photochemical smog. Note that some pollutants may be both primary andsecondary: that is, they are both emitted directly and formed from other primary pollutants.
Major primary pollutants produced by human activity include: Nitrogen oxides (NOx) - especially nitrogen dioxide are emitted from high temperature combustion. This reddish- brown toxic gas has a characteristic sharp, biting odor. NO2 is one of the most prominent air pollutants. Sulfur oxides (SOx) - especially sulfur dioxide. SO2 is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide. Further oxidation of SO2 , usually forms H2SO4, and thus acid rain. This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
Sulfur and nitrogen oxides from powerplants, industry, cars and other sources causerain, snow and fog to become acidic. The most serious damage caused by acidrain today is acidification of water lakes andrivers. In some cases they become so acidicthat they can no longer support fish and theirfood chains. Forest health can also be affected fromthis in areas where the soils are being acidified.
Major primary pollutants produced by human activity Carbon monoxide - is a colorless, odorless, non-irritating but very poisonous gas. It is a product by incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide. Carbon dioxide (CO2) - a greenhouse gas emitted from combustion but is also a gas vital to living organisms. It is a natural gas in the atmosphere. Volatile organic compounds - VOCs are an important outdoor air pollutant. In this field they are often divided into the separate categories of methane (CH4) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. Within the NMVOCs, the aromatic compounds benzene, toluene and xylene are suspected carcinogens and may lead to leukemia through prolonged exposure.
Major primary pollutants produced by human activity Particulate matter (PM) - particulates, or fine particles, are tiny particles of solid or liquid suspended in a gas. Sources of particulate matter can be man made or natural.• Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray.• Human activities, such as the burning of fuels in vehicles, power plants and various industrial processes also generate significant amounts of aerosols.
Averaged over the globe, anthropogenicaerosols currently account for about 10 percent of the total amount of aerosols in our atmosphere.Increased levels of fine particles in the air arelinked to health hazards such as heart disease, altered lung function and lung cancer.
Major primary pollutants produced by human activity Toxic metals, such as lead, cadmium and copper. Chlorofluorocarbons (CFCs) - harmful to the ozonelayer emitted from products currently banned from use. Ammonia (NH3) - emitted from agriculturalprocesses. Ammonia contributes significantly to thenutritional needs of terrestrial organisms by serving as aprecursor to foodstuffs and fertilizers. Although in wideuse, ammonia is both caustic and hazardous.
Major primary pollutants Odors - such as from garbage, sewage, and industrial processes Radioactive pollutants - produced by nuclear explosions, war explosives, and natural processes such as the radioactive decay of radon.
Secondary pollutants include: Particulate matter formed fromgaseous primary pollutants andcompounds in photochemical smog. Smog is a kind of air pollution; theword "smog" is a portmanteau of smokeand fog. Industrial or gray smog is consideredthe most serious type of air pollution.
Classic smog results from smoke andoxides of that are released by burning coaland oil containing minor amounts of sulfur. The smoke gives the air a gray color.Industrial smog has been known to causeair pollution disasters. One of the worstoccurred in London in December of1952. Five days of stagnant air broughtabout high-pressure systems causedbetween 3,500 and 4,000 deaths.
Modern smog does not usually come from coal but from vehicularand industrial emissions that are acted on in the atmosphere by sunlight to form secondary pollutants that alsocombine with the primary emissions to form photochemical smog (also know as brown smog).
Ozone in the in the upper level occursnaturally and protects life on earth butozone at ground level is a noxiouspollutant. Ozone (O3) is a key constituent of thetroposphere (it is also an importantconstituent of certain regions of thestratosphere commonly known as theOzone layer).
Secondary pollutants include: Ground level ozone (O3) is secondary pollutant formed in the atmosphere through a complex set of chemical reactions involving hydrocarbons, oxides of nitrogen, and sunlight. It is the major component of photochemical smog and presents the most intractable urban air quality problem. Photochemical and chemical reactions involving it drive many of the chemical processes that occur in the atmosphere by day and by night. The rate at which the reactions proceed is related to both temperature and intensity of the sunlight. Peroxyacetyl nitrate (PAN) - formed from NOx and VOCs.
Sources of air pollution Sources of air pollution refer to the variouslocations, activities or factors which areresponsible for the releasing of pollutants inthe atmosphere. These sources can be classified intotwo major categories which are:
Natural sources Dust from natural sources, usually large areas of land with little or no vegetation. Methane, emitted by the digestion of food by animals, for example cattle. Smoke and carbon monoxide from wildfires. Volcanic activity, which produce sulfur, chlorine, and ash particulates.
Natural sources• - Radon gas from radioactive decay within the Earths crust.• Radon is a colorless, odorless, naturally occurring, radioactive noble gas that is formed from the decay of radium. It is considered to be a health hazard. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as the basement and it is the second most frequent cause of lung cancer, after cigarette smoking.
Anthropogenic sources (humanactivity) mostly related to burningdifferent kinds of fuel: "Stationary Sources" includesmoke stacks of power plants,factories and waste incinerators, aswell as furnaces and other types offuel-burning heating devices.
Combustion of fuel to generate heat andpower produces sulfur dioxide, nitrogen oxides,hydrocarbons, polynuclear aromatichydrocarbons, dust, fly ash and smoke and thecarcinogenic 3,4-benzepyrenes. Domestic combustion of coal, wood or oilis also a major source of these pollutants. Many industries discharge carbonmonoxide, carbon dioxide, hydrogen sulfide,sulfur dioxide, hydrogen fluoride, hydrochloricacid, dust, ozone.
Anthropogenic sources "Mobile Sources" include motor vehicles, marine vessels, aircraft etc. Automobiles are the major source of air pollution in urban areas. They emit hydro- carbons, carbon monoxide, lead, nitrogen oxides and particulate matter. In strong sunlight and UV-radiation certain of these hydrocarbons and oxides of nitrogen may be converted in the atmosphere into “photochemical” pollutants of oxidizing nature.
-Chemicals, dust and controlled burnpractices in agriculture and forestrymanagement. Controlled or prescribedburning is a technique sometimes used inforest management, farming, prairierestoration. Controlled burning stimulates thegermination of some desirable forest trees,thus renewing the forest.- Fumes from paint, hair spray, varnish,aerosol sprays and other solvents- Military - such as nuclear weapons, toxicgases.
• Waste deposition in landfills, whichgenerate methane. Methane is not toxic; however, it ishighly flammable and may formexplosive mixtures with air. Methane isalso an asphyxiant and may displaceoxygen in an enclosed space. Asphyxia orsuffocation may result if the oxygenconcentration is reduced to below 19.5%by displacement.
Meteorological factors The level of atmospheric pollutionat any time depends upon meteorologicalfactors, e.g. topography, air movementand climate. Winds help in the dispersaland dilution of pollutants. If the topography is dominated bymountains (or tall buildings) the windsbecome weak and calm, and pollutantstend to concentrate in the breathing zone.
The vertical diffusion of pollutants dependsupon the temperature gradient. When there is arapid cooling of lower layers of air (temperatureinversion) there is a little vertical motion and thepollutants and water vapours remain trapped atthe lower levels and the result is “smog” – thisway the temperature inversion is a threat tohuman health. All the mentioned factors must be carefullystudied prior to location of industrial factoriesnear towns and villages and a certain distanceshould be kept to avoid health problems of theresidents.
Effects of air pollutants Many urban residents are exposed to airpollution level above the recommended limits.In many developing countries air quality hasdeteriorated because of raising industrialactivity, increasing power generation and thecombustion of streets with poorly maintainedautomobiles that use leaded fuel.Air pollution can affect by two main ways:
1. Health aspects. The health effectsare both immediate and delayed. The immediate effects are borne bythe respiratory system, the resultingstate is acute bronchitis. If the airpollution is intense, it may result evenimmediate death by suffocation. The delayed effects most commonlyare chronic bronchitis, lung cancer,bronchial asthma and respiratoryallergies.
Precise estimates of the risk of airpollution to health are difficult toquantify because of problems inestimating the degree of exposure ofindividuals and the influence of possiblecompounding variables such as nutrition,smoking, occupation and climate. The elderly, children, smokers andthose with chronic respiratory difficultiesare most vulnerable.
Major air pollutants, their sources and adverse effectsNoxious agent Sources Adverse effectsOxides of nitrogen Automobile exhaust, Respiratory tract irritation, combustion of fuel to generate bronchial hyperactivity, heat and power, gas and wood impaired lung defences, stoves, many industries bronchialitis obliteransHydrocarbons Automobile exhaust, Lung cancer combustion of fuel to generate heat and power, cigarette smokeOzone Automobile exhaust, high Cough, substernal discomfort, attitude aircraft cabins bronchoconstriction, respiratory tract irritationSulfur dioxide Combustion of fuel to generate Exacerbation of asthma, heat and power, smelters, oil respiratory tract irritation refineriesLead Automobile exhaust using Impaired neuropsychological leaded gasoline development in children
Effects of air pollutants 2. Social and economic aspects. Air pollution generates various economic losses but their detailed estimation is extremely difficult. They may be divided into four groups: expenses for air quality protection; expenses generated by the worse health condition of the society; losses of raw materials which become air pollution; losses caused by the increased corrosion of machines, buildings, and damage of historical buildings and monuments.
Effects of air pollutants Anthropogenic global warming (AGW),a recent warming of the Earths loweratmosphere as evidenced by the global meantemperature anomaly trend, is believed to be theresult of an "enhanced greenhouse effect"mainly due to human-produced increasedconcentrations of greenhouse gases in theatmosphere and changes in the use of land.
The greenhouse effect refers tothe change in the steady statetemperature of a planet or moonby the presence of an atmospherecontaining gas that absorbs andemits infrared radiation.
Greenhouse gases include water vapor,carbon dioxide and methane. The greenhouse effect, is generallybelieved to come from the build up of carbondioxide (CO2) gas in the atmosphere. Plants convert carbon dioxide back tooxygen, but the release of carbon dioxidefrom human activities is higher than theworlds plants can process. The situation ismade worse since many of the earths forestsare being removed, and plant life is beingdamaged by acid rain.
Basic mechanism The Earth receives energy from the Sun mostly in the form of visible light. The bulk of this energy is not absorbed by the atmosphere since the atmosphere is transparent to visible light. 50% of the suns energy reaches theEarth which is absorbed by the surface asheat. Because of its temperature, the Earthssurface radiates energy in infrared range.
Basic mechanism The Greenhouse gases are not transparentto infrared radiation so they absorb infraredradiation. They warm the atmosphere by efficientlyabsorbing thermal infrared radiation emitted bythe Earth’s surface, by the atmosphere itself,and by clouds. As a result of its warmth, the atmospherealso radiates thermal infrared in all directions,including downward to the Earth’s surface.
Basic mechanism Thus, greenhouse gases trap heatwithin the surface-troposphere system. Infrared radiation is absorbed from alldirections and is passed as heat to all gasesin the atmosphere. The atmosphere alsoradiates in the infrared range (because of itstemperature, in the same way the Earthssurface does) and does so in all directions.
The surface and lower atmosphere arewarmed because of the greenhouse gases andmakes our life on earth possible. In the absence of the greenhouse effectand an atmosphere, the Earths averagesurface temperature of 14 °C (57 °F) could beas low as −18 °C (−0.4 °F). In our solarsystem, Mars, Venus, and the moon Titan alsoexhibit greenhouse effects according to theirrespective environments. In addition, Titanhas an anti-greenhouse effect and Plutoexhibits behavior similar to the anti-greenhouse effect.
This mechanism is fundamentally different from the mechanism of anactual greenhouse, which instead isolatesair inside the structure so that the heat isnot lost by convection and conduction.
Effects of air pollutants Stratospheric ozone depletion due toair pollution has been recognized as athreat to human health as well as to theEarths ecosystems. The ozone layer in the stratosphereprotects the earth from harmful ultravioletradiation from the sun.
Ozone depletion describes twodistinct, but related observations:- a slow, steady decline of about 4 percentper decade in the total volume of ozone inEarths stratosphere (ozone layer) since thelate 1970s, and- a much larger, but seasonal, decrease instratospheric ozone over Earths polarregions during the same period.
The latter phenomenon is commonlyreferred to as the ozone hole. In addition tothis well-known stratospheric ozonedepletion, there are also tropospheric ozonedepletion events, which occur near the surfacein polar regions during spring. The detailed mechanism by which thepolar ozone holes form is different from thatfor the mid-latitude thinning, but the mostimportant process in both trends is catalyticdestruction of ozone by atomic chlorine andbromine.
The main source of these halogen atoms in thestratosphere is photodissociation ofchlorofluorocarbon (CFC) compounds,commonly called freons, and of bromo-fluorocarbon compounds known as halons. These compounds are transported intothe stratosphere after being emitted at thesurface. They are released from aerosolsprays, polystyrene containers, refrigeratorcoolant and air conditioning units. Both ozonedepletion mechanisms strengthened asemissions of CFCs and halons increased.
CFCs and other contributory substancesare commonly referred to as ozone-depletingsubstances (ODS). Since the ozone layer prevents mostharmful UVB wavelengths (270–315 nm) ofultraviolet light from passing through theEarths atmosphere, observed and projecteddecreases in ozone have generated worldwideconcern leading to adoption of the MontrealProtocol banning the production of CFCs andhalons as well as related ozone depletingchemicals such as carbon tetrachloride andtrichloroethane.
It is suspected that a variety ofbiological consequences such as increasesin skin cancer, damage to plants, andreduction of plankton populations in theoceans photic zone may result from theincreased UV exposure due to ozonedepletion.
Consequences of ozone layer depletion Increased UV Although decreases in stratospheric ozone arewell-tied to CFCs and there are good theoreticalreasons to believe that decreases in ozone will leadto increases in surface UVB, there is no directobservational evidence linking ozone depletion tohigher incidence of skin cancer in human beings. This is partly due to the fact that UVA, whichhas also been implicated in some forms of skincancer, is not absorbed by ozone, and it is nearlyimpossible to control statistics for lifestyle changesin the populace.
Because it is this same UV radiation thatcreates ozone in the ozone layer from O2(regular oxygen) in the first place, a reductionin stratospheric ozone would actually tend toincrease photochemical production of ozone atlower levels (in the troposphere), although theoverall observed trends in total column ozonestill show a decrease, largely because ozoneproduced lower down has a naturally shorterphotochemical lifetime, so it is destroyed beforethe concentrations could reach a level whichwould compensate for the ozone reductionhigher up.
Effects of ozone layer depletion on humansradiation absorbed by UVB (the higher energy UVozone) is generally accepted to be a contributory factor toskin cancer. In addition, increased surface UV leads toincreased tropospheric ozone, which is a health risk tohumans. The increased surface UV also represents anincrease in the vitamin D synthetic capacity of thesunlight. The cancer preventive effects of vitamin D representa possible beneficial effect of ozone depletion. In terms ofhealth costs, the possible benefits of increased UVirradiance may outweigh the burden.
Effects of ozone layer depletion on humans 1. Basal and Squamous Cell CarcinomasThe most common forms of skin cancer in humans,have been strongly linked to UVB exposure. Themechanism by which UVB induces these cancers iswell understood — absorption of UVB radiationcauses the pyrimidine bases in the DNA moleculeto form dimers, resulting in transcription errorswhen the DNA replicates. By combiningepidemiological data with results of animal studies,scientists have estimated that a one percentdecrease in stratospheric ozone would increase theincidence of these cancers by 2%.
2. Malignant Melanoma - Another form ofskin cancer, is much less common but farmore dangerous, being lethal in about 15% -20% of the cases diagnosed. The relationshipbetween malignant melanoma and ultravioletexposure is not yet well understood, but itappears that both UVB and UVA areinvolved. Experiments on fish suggest that 90to 95% of malignant melanomas may be dueto UVA and visible radiation whereasexperiments on opossums suggest a largerrole for UVB.
Because of this uncertainty, it is difficultto estimate the impact of ozone depletion onmelanoma incidence. One study showed that a10% increase in UVB radiation wasassociated with a 19% increase in melanomasfor men and 16% for women. A study ofpeople in Punta Arenas, at the southern tip ofChile, showed a 56% increase in melanomaand a 46% increase in nonmelanoma skincancer over a period of seven years, alongwith decreased ozone and increased UVBlevels.
3. Cortical Cataracts - Studies aresuggestive of an association between ocularcortical cataracts and UV-B exposure. 4. Increased Tropospheric Ozone -Increased surface UV leads to increasedtropospheric ozone. Ground-level ozone isgenerally recognized to be a health risk, dueto its strong oxidant properties. At this time,ozone at ground level is produced mainly by theaction of UV radiation on combustion gasesfrom vehicle exhausts.
Prevention activities The problem of air pollution isworldwide and transcends nationalboundaries. Though air pollution is still a seriousproblem, in many countries in the world,steps are being taken to stop thedamage to our environment from airpollution.
Many electric power plants, factories,and facilities that burn wastes areequipped with devices called scrubbers.Scrubbers remove sulfur dioxide and otherpollutants before the wastes are releasedinto the air. Also, todays cars are designed tocreate less pollution. Many are equippedwith anti-pollution devices called catalyticconverters, which reduce the amount ofpollution from automobile engines.
Most polluted cities Air pollution is usually concentratedin densely populated metropolitan areas,especially in developing countries whereenvironmental regulations are relatively laxor nonexistent. However, even populated areas indeveloped countries attain unhealthy levelsof pollution.
Most Polluted World Cities by PMParticulate matter, City μg/m³ (2004) 169 Cairo, Egypt 150 Delhi, India 128 Kolkata, India (Calcutta) 125 Tianjin, China 123 Chongqing, China 109 Kanpur, India 109 Lucknow, India 104 Jakarta, Indonesia 101 Shenyang, China
Carbon dioxide emissions Total CO2 emissions 106 Tons of CO2 per year:• United States: 2, 795• China: 2,680• Russia: 661• India: 583• Japan: 415• Germany: 356• Australia: 300• South Africa: 232• United Kingdom: 212• South Korea: 185
Per capita CO2 emissions Tons of CO2 per year per capita:• Australia: 10• United States: 8.2• United Kingdom: 3.2• China: 1.8• India: 0.5