AIR POLLUTION. Atmospheric Composition: Stratification of Atmosphere

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1 Atmspheric Cmpsitin: AIR POLLUTION Dry air within several kilmeters f grund level cnsists f 2 majr cmpnents Nitrgen, 78.8 % Oxygen, % 2 minr cmpnents Argn, 0.934% CO 2, 0.035% Nen, kryptn, helium, xenn Stratificatin f Atmsphere T=-1200 C T=-92 C P=3x10-4 atm T=-2 C P= atm T=56 C P = 0.1 atm T = 15 C, P= 1 atm

2 Trapsphere The lwest layer f the atmsphere Extends frm sea level t an altitude f km Hmgenus cmpsitins f majr gases Hmgenus cmpsitin results frm cnstant mixing by circulating air masses. Water vapr cntent f the trpsphere is extremely variable because f clud frmatin, precipitatin and evapratin f water frm terrestrial water bdies. Stratsphere- Maximum temperature : -2 C Temperature increases with increase altitude This phenmenn is due t O 3, which may reach a level arund 10 ppm by vlume in the mid range f stratsphere. Air pllutin

3 presence f chemicals in the atmsphere in quantities and duratin that are harmful t human health and the envirnment Types f air pllutants: Primary pllutants - prducts f natural events (like fires and vlcanic eruptins) and human activities added directly t the air Secndary pllutants - frmed by interactin f primary pllutants with each ther r with nrmal cmpnents f the air Surces f Air Pllutin Fssil Fuel based Pwer Plants Fssil fuels prvide abut 90% f energy used wrldwide; they are at the same time the biggest surce f air pllutin. Burning fssil fuels turns carbn t carbndixide (a greenhuse gas) and a small amunts f carbn mnxide (a txic gas). Bth cal and fuel il cntain abut 1-5% f sulfur. When burned, sulfur is xidized t sulfurdixide ( a txic gas ) and emitted t the atmsphere. Cmbustin prcess, taking places at temperatures higher than 1000 C, generated als nitrgen xides (txic gases). Pwer plants that wrk n cal and fuel il cnsume immense amunts f cmbustible material, prducing particularly large amunts f air pllutants. Industry

4 Besides pwer plants, the majr air plluters are chemical industry petrleum industry pulp and paper industry metallurgical industry and cement industry. Their emissins include sulfur dixide (SO 2 ), nitrgen xides (NO x ) carbn mnxide (CO), particulate matter (PM 10 ), hydrgen sulfide (H 2 S), hydrgen chlride, hydrgen fluride, all types f vlatile rganic carbns, and metal particles. Tday s technlgy is able t remve abut 90-99% f them frm emissins. Incineratrs

5 Incineratin f slid waste als generates a range f air pllutants, cmprising cnventinal cmbustin gases, particulate matter (including heavy metals), plynuclear armatic hydrcarbns (PAHs), such as dibenzdixins (PCDDs), dibenzefurans (PCDFs) and biphenyls (PCBs), are particularly txic and ptentially mutagenic. Mtr Vehicles Exhaust gases frm mtr vehicles cntain carbndixide,- carbn mnxide, nitrgen xides, traces f hydrcarbns frm unburnt fuel, particulate lead (if gasline cntains tetraethyl lead), sulfur dixide (if diesel fuel is used) and PM 10 (very small particles less than 10 micrns acrss) Indr Pllutants Certain substances are far mre cncentrated in the indr envirnment than utdrs. The fremst indr air pllutant is radn, an drless, clrless and tasteless radiactive gas. In cnfined spaces, such as basements f huses, radn can accumulate and reach hazardus levels. If sil cntain uranium in high amunts and if the huse built n such sil has pr ventilatin, then radn cncentratins may be exceptinally high.

6 Other indr pllutants are carbn mnxide, nitrgen dixide, particulate matter, ply nuclear armatic hydrcarbns (PAHs) frm wd stves and fire-places, frmaldehyde frm plywd and wall paper, asbests frm fire insulating and nise reducing material and pesticides frm husehld pest cntrl activities.

7 Classificatin f Pllutants Majr Classes Subclasses Typical Members f subclasses Particulates Slid Dust, smke, fumes, fly ash Liquid Mist, spray Gases Organic Hydrcarbns Hexane, benzene, ethylene, butane Aldehydes and Frmadehyde, ketnes acetne Other rganics Chlrinated hydrcarbns Inrganic Oxides f carbn Carbn mnxide, carbn dixide Oxides f sulfur Sulfur dixide, sulfur trixide Oxides f nitrgen Nitrgen dixide, nitric xide Other inrganics Hydrgen sulfide, hydrgen fluride, ammnia

8 Majr Classes f Air Pllutants: Carbn xides (CO & CO2) surces = incmplete cmbustin f fssil fuels transprtatin, industry, & hme heating CO2 is an imprtant greenhuse gas CO (carbn mnxide) the mst abundant pllutant knw t affect human health cmbines with hemglbin & may create prblems fr infants, the elderly, & thse with heart r respiratry diseases Clrless, tasteless and drless, carbn mnxide gas is chemically inert under nrmal cnditins and has an atmspheric mean life f abut 2 ½ mnths. it can seriusly affect human aerbic metablism, wing its high affinity fr hemglbin, the cmpnent f the bld respnsible fr the transprt f xygen. Carbn mnxide reacts with the hemglbin (Hb) f bld t give carbxyhemglbin (COHb), thus reducing the capability f the bld t carry xygen. the affinity f hemglbin fr carbn mnxide is mre than 200 times as great as its affinity fr xygen, CO can seriusly impair the transprt f O 2, even when present at lw cncentratins. Surces : Carbn mnxide surces are bth natural and anthrpgenic.

9 Argnne Natinal Labratry reprts 3 ½ billin tnes f CO are prduced in nature yearly by the xidatin f methane gas frm decaying vegetatin. Surces and quantities f carbn mnxide Emissins, 10 6 tnes/year Surce 1980 Transprtatin 69.1 Fuel cmbustin in statinary surces 2.1 (pwer and heating) Industrial Prcesses 5.8 Slid waste dispsal 8.4 and miscellaneus

10 Sulfur xides (mainly SO2, r sulfur dixide) surce = cmbustin f cal & il (esp. cal) SO2 released in the U.S. cmes frm: utilities 69.5% industrial manufacturing prcesses 12.7% industrial cmbustin 11.6% transprtatin 3.7% ther surces 2.5%. can react with gases in atmsphere t frm sulfuric acid ('acid rain') 20 millin tns released in U.S. every year The xides f sulfur (SO x ) are prbably the mst widespread and the mst intensely studied f all anthrpgenic air pllutants. They include six different gaseus cmpunds: Sulfur mnxide (SO) Sulfur sesquixide (S 2 O 3 ) Sulfur dixide (SO 2 ) Sulfur heptxide (S 2 O 7 ) Sulfur trixide (SO 3 ) Sulfur tetraxide (SO 4 ) sulfur dixide and sulfur trixide are the tw xides f sulfur f mst interest Sulfur dixide is a clrless, nnflammable, and nnexplsive gas.

11 SO 2 remains airbne an average f 2 t 4 d, during which time it may be transprted as far as 1000 km. Thus the prblem f SO 2 pllutin can becme an internatinal ne. SO 2 can react with the water t frm sulfurus acid, a weak acid which can react directly with rganic dyes. SO 2 H2O H2SO3 + sulfurus acid SO 3 can react with the water t frm sulfurus acid, a weak acid which can react directly with rganic dyes. SO 3 H 2O H2SO4 + sulfuric acid Effects f Sulfur xides tend t irritate mucus membranes f the respiratry tract and fster the develpment f chrnic respiratry diseases. In a dusty envirnment, SO 2, is particularly harmful because bth sulfur dixide and sulfuric acid mlecules paralyze the hair like cilia which line the respiratry tract. Withut the regular sweeping actin f the cilia, particulates are able t penetrate t the lungs and settle there. These particulates carry with them the cncentrated amunts f SO 2, thus bringing this irritant int direct, prlnged cntact with the delicate lung tissues. Sulfuric acid aersls will readily attack building materials, especially thse cntaining carbnates such as marble, limestne, rfing slate

12 and mrtar. The carbnates are replaced by sulfates which are sluble in water CaCO3 + H2SO4 CaSO4 + CO2 + H2O Many f the histrical mnuments, public buildings, cathedrals have deterirated frm expsure t the by-prducts f sulfur dixides. Excess expsure t SO 2 accelerates crrsin rates fr many metals such as irn, zinc, cpper and nickel especially at relative humidities ver 70%.

13 Nitrgen xides - NO (nitric xide) & NO2 (nitrgen dixide) surce = mtr vehicles & industry (burning fssil fuels) can react with ther gases in atmsphere t frm nitric acid (HNO3) ('acid rain') Oxides f nitrgen (NO x ) include six knwn gaseus cmpunds: nitric xide (NO), nitrgen dixide (NO 2 ), nitrus xide (N 2 O), nitrgen sesquixide (N 2 O 3 ), nitrgen tetrxide (N 2 O 4 ) and nitrgen pentxide (N 2 O 5 ) The tw xides f nitrgen f primary cncern in air pllutin are nitric xide (NO) and nitrgen dixide (NO 2 ), the nly tw xides f nitrgen that are emitted in significant quantities t the atmsphere. 2NO + H O HNO + HNO nitrus acid 2 2 3NO H O HNO + NO nitric xide

14 Secndary Pllutants f NO PHOTOSMOG Phtchemical smg In bright sunlight nitrgen xides hydrcarbns and xygen interact chemically t prduce pwerful xidants like zne (O 3 ) and perxyacetyl nitrate (PAN). These secndary pllutants are damaging t plant life and lead t the frmatin f phtchemical smg. PAN is primarily respnsible fr the eye irritatin s characteristic f this type f smg. The figure utlines representative reactins leading t the frmatin f phtchemical smg. Radicles are atms r mlecules with unpaired electrns. They are very reactive chemically. The catalytic cnverter in autmbile exhaust systems reduces air pllutin by xidizing hydrcarbns t CO 2 and H 2 O and, t a lesser extent, cnverting nitrgen xides t N 2 and O 2.

15 PHOTOSMOG was bserved fr the first time in Ls Angeles abut 50 years ag. present in all metrplitan areas where heavy rad traffic is accmpanied by clear skies and stagnant atmsphere (sunny day & n wind). The sequences f the steps leading t pht smg starts with the frmatin f nitrgen xides prduced by car engines r during any ther cmbustin prcess. 2 NO + O 2 2 NO 2 sun 2 NO 2 NO + O{ Atmic Oxygen 2 NO 2 sun NO + O { Atmic Oxygen O + O2 O3 ( Ozne) O 3 + NO O2 + NO2 Hydrcarbn + O RO2 123 alkylperxy radicals RO + NO 2 NO 2 RO2 + O2 + NO2 Perxyacyl nitrate( PAN)

16 EFFECTS OF OZONE Althugh zne in the stratsphere is essential t sustain life, its presence in the lw trpsphere is extremely hazardus. The zne mlecules xidize matter and destry vegetatin. Its inhalatin by humans and animals cause acute and chrnic prblems f the respiratry tract and lungs, which in turn