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    Particulate Matter Air Pollution

    andHealth Risks

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    Tiny solid or liquid particles- other than those of pure water- that are temporarily suspended in air and that are usually individually invisible to the

    naked eye.

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    Wh at is Particulate Matter?

    Particulate matter (PM) describes awide variety of airborne material. PMpollution consists of materials

    (including dust, smoke, and soot),that are directly emitted into the air or result from the transformation of gaseous pollutants.Particles come from naturalsources (e.g., volcanic eruptions)and human activities such asburning fossil fuels, incineratingwastes, and smelting metals.

    Image from http://www.epa.gov/eogapti1/module3/distribu/distribu.htm

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    Wh ere Does PM Originate?

    VOCsNO 2

    SO 2

    S ources may emit PM directly into the environment or emit p recursorssuch as sulfur dioxide (SO 2), nitrogen dioxide (NO 2), and volatileorganic com p ounds (VOCs), which are transformed throughatmospheric chemistry to form PM.

    A mmonia (NH 3)

    A mmonia (NH 3)

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    S ources of PM and PM Precursors

    Mobile Sources(vehicles)

    VOCs, NO 2, PM

    Stationary Sources(power plants, factories)NO 2, S O2, PM

    Area Sources(drycleaners, gas stations)


    Natural Sources(forest fires, volcanoes)


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    Determinants of PM Concentration

    Weather patternsW indS tability (vertical movement of air)TurbulencePrecipitationTopographyS mokestack height and temperature of gases

    Nearby natural and built structures may lead to downward movingcurrents causing aerodynamic or building downwash of smokestack emissions.

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    T h e Role of Inversions

    An inversion is an extremelystable layer of theatmosphere that forms over areas.Temperature inversions trappollutants close to the ground.These inversions involvelayers of hot air sitting above

    cooler air near ground level.When particles accumulate inthe air layer, they are unableto rise into the atmospherewhere winds will dispersethem.

    S ource: http://www.epa.gov/apti/ course422/ce1.html

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    S ize and s h ape of PM

    PM are not of same size, shape and chemical composition.Not all the PM are spherical but conventionally they aresupposed to be.

    Diameter of particles is the most important property itdecides Coarse and fine depending upon their diameter less than or greater than 2. 5 m.2nm to 100 m is the range of diameter.

    Aerosol is a collection of particulates, whether solid or liquiddroplets, dispersed in air and having very small size lessthan 100 m

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    E stablishing a particle sizedefinition for irregularly shapedparticles necessitates the use of astandardized measure referred to

    as the aerodynamic diameter,measured in microns or micrometers ( m)

    The graph at the right shows thedistribution of the 4 main particlesize categories, By comparison, ahuman hair is approximately 7 0 microns in diameter.

    Particulate Matter:Aerodynamic Diameter

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    S tokes Law

    The rate, in distance per second, at which particles settleincreases with the square of their diameter. i.e. a particle half the diameter of another falls four time

    more slowly.

    Fine particulates usually remain airborne for days or

    weeks, whereas coarse particulates settle out fairly rapidly.

    Incorporation in raindrops.

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    S ources of Coarse particles(Mostly Primary PM)

    Natural:Mineral from earth : Dust from soil or rock with elementalcomposition of Al, Ca, S i and O in the form of aluminiumsilicates.W ind storm in desertsW ind also generate coarse particles by the mechanicaldisintegration of leaf litter.PollensW ildfires and volcanic eruptionsNaCl near and above the sea.

    Anthro p ogenic sources: S tone crushing, overgrazing,deforestation, land cultivation(soil erosion)

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    S ources of fine particles(Mostly S econdary PM)

    Primary fine particles from anthropogenic origin includeones generated by the wearing of tires and vehicle brakesas well as the dust from metal smelting.

    Exhaust from vehicles: The incomplete combustion of fuels such as coal, oil, gasoline and diesel produces manyfine particles, which are mainly crystallites of carbon.

    Type of exhaust in Dielsel versus petrol?

    Why fine particles are called S econdary?

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    Organics: reaction between VOCs and Nitrogen oxides inPC smog, partially oxidized to carboxylic acids, aromatichydrocarbons with at least 7 carbons (e.g. toulene) from the

    evaporation of gasoline and other HCs having less than 7carbons with substantial vapor pressure.

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    Inorganic Com p ounds: compounds of sulfur and Nitrogen.Sulfur:

    as dimethyl sulfide (CH 3)2S emitted from oceans.A biproduct of its oxidation in air is C arbonyl sulfide , CO S .Both the (CH 3)2S and H 2S are oxidized to S O 2.S O 2 is also released by volcanoes. In a period of hours todays it gets converted into sulfuric acid and sulfates in air.

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    Acid Base nature of Fine particles

    Fine particle in many area are acidic , due to their content of sulfuric and nitric acids.Nitric Acid: E nd product of Oxidation of Nitrogen

    containing gas such as NH 3, NO and NO 2.Both the acids undergo acid-base reaction with ammoniawhich form soluble salts of ammonium sulfate,((NH 4)2S O 4), ammonium nitrate, (NH 4NO 3).

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    S ources of Ammonia

    From biological decayAnimal urineUse of fertilizers etc.

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    On evaporation of water, these salts become solidparticles with predominant anions of sulfate, ( S O 42-),bisulfate (H S O 4 -),and Nitrate (NO 3-):

    And Cations of ammonium (NH 4+) and Hydrogen (H +)

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    S ummary

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    T h e PM Indices

    It is a measure of concentration of suspended particles, i.e.the amount of particulate matter that is present in a givenvolume.Usual concentration unit is g/m


    The cut-off diameter, in m, is listed as subscript to PM.

    PM 10 : inhable

    PM 2.5 : respirable

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    S ize is important to the behavior of PM in the atmosphereand human body and determines the entry and absorptionpotential for particles in the lungs.Particles larger than 10 Q m are trapped in the nose andthroat and never reach the lungs.Therefore, particles 10 Q m in diameter or less are of mostconcern for their effects on human health.Particles between 5 and 10 Q m are removed by physicalprocesses in the throat.Particles smaller than 5 Q m reach the bronchial tubes,while particles 2. 5 Q m in diameter or smaller are breathedinto the deepest portions of the lungs.

    Particulate Matter:S ize Matters

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    Premature deathLung cancer Development of chronic lung diseaseHeart attacksRespiratory symptoms and medication use inpeople with chronic lung disease and asthmaDecreased lung functionPre-term birthLow birth weight

    Wh at Adverse Healt h EffectsHave Been Linked to PM?

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    e.g. Photochemical smog (yellowish-brownish-grayhaze)Particle size 0 .4-0 .8 m can scatter light and interferewith its transmission, thereby reducing visual clarity, longdistance visibility and amount of sunlight reaching earth.0 .1-1 .0 m produces haze.