Atmospheric Chemistry.ppt

1、Atmospheric Chemistry,Formation of the Atmosphere The Early Atmosphere Origin of Life and Oxygen Ozone Air Pollution Acid Rain Greenhouse Effect,Formation of the Earth,Apollo Space Program (1960s) Otto Schmidt Cosmic Dust Planet (100 million years) Ball 10 km 12,000 km Heat Generated during the Proc

2、ess( Collisions )Differentiation Occurs,Thermal Consequences,Earths Core Molten Fe ( Density 7.86 g/cc)Ni ( Density 8.9 g/cc)Outer ShellFe2O3 / FeO ( Density 5.2/5.7 g/cc)Si/SiO2 (Density 2.33/2.32 g/cc)Al/Al2O3 ( Density 2.7/3.5 g/cc),Formation of the Mantle,The less dense material will go toward t

3、he surface (Polar Oxides of Si, Al, Fe) Separation will occur as Fe/Ni core is nonpolarMANTLEstarts to form and cool(Production of Iron from Iron Ore),Isotope Distribution of the Earth,Investigation of the History of the Earth primarily relied on isotope analysis.Decay of 238U 206PbDecay of 235U 207

4、PbAnd the rare gases He, Ar, Xe 4.5 Billion years Old,Appearance of the Atmosphere,Did the atmosphere suddenly appear ? Isotope Analysis gives a clueClaude Allegre He, Ar & Xe( Rare Gases do not react readily )Argon has three isotopes(36Ar 0.337) (38Ar 0.063) (40Ar 99.60) EC Decay 40K 40Ar ( t1/2 =

5、1.28 x 109y ),Isotopes of Xe,Xenon has 9 isotopes With the following distribution124Xe 0.1% , 126Xe 0.09%, 128Xe 1.91% 129Xe 26.4%, 130Xe 4.1%, 131Xe 21.2%132Xe 26.9%, 134Xe 10.4%, 136Xe 8.9%,Distribution of Xe isotopes,Nucleosynthesis gives rise to 129Xe- Decay of 129I 129Xe(t1/2 = 1.6 x 107y) The

6、distribution of Xe isotopes in the mantle and atmosphere can give information about the Earths Atmosphere as the outgassed distribution will vary to that of the mantle.,Differentiation,The Atmosphere was formed due to OUT GASSING of the mantle (Heat)& Volcanic Activity The Mantle does not contain an

7、y40K or 129I All 129 Xe in mantle came from 129I,Age of differentiation,From the ratio of 129 Xe in the Mantle to that of 129 Xe in the Atmosphere it possible to gain some idea of the age of differentiation as the Xe due to Nucleosynthesis would have been OUTGASSED into the atmosphere.,Ratios of Iso

8、topes,The Argon trapped in Mantle evolved from the radioactive decay of 40K 40K The Xenon trapped in Mantle evolved from the radioactive decay of 129IThe ratio of the amount in the mantle to the atmosphere can give information about the process of differentiation,Conclusions from Isotope Analysis, I

9、f outgassing occurred at the beginning the atmosphere would not contain 40Ar 4rBut would contain 129XeResults and Calculations indicate80% to 85% of the Earths Atmosphere was outgassed in the first million years,Collecting the evidence,The other 15% has arisen due to slow release over 4.4 billion ye

10、arsDifficult Analytical Problem requiring Concentration of the samplesSpecific Choice of Sampling Sites,Early Atmosphere,Majors: CO2, N2, H2O (Water Vapour)Traces: CH4, NH3, SO2, HClWater Vapour OceansFeO/Fe2O3 (Grand Canyon) indicatesO2 emerged in the atmosphere about 2 billion years ago,Origin of

11、Life,Stanley Miller (1950) “ Early Earth ”Experimental Setup CH4, NH3, H2, H2O(g) ( Atmosphere) H2O(l) ( Oceans) Electrode discharge (Simulate Lightning)Analysis of Fractions,Formation of Simple Amino Acids,Glycine was found How Glycine (NH2CH2COOH) Formed HCOH + NH3 + HCN NH2CH2CN + H2O Formaldehyd

12、e Cyanide Hydrogen AminonitrileNH2CH2CN + 2 H2O NH2CH2COOH + NH3,Murchison Meteor,A number of the compounds discovered in the discharge fractions are precursors to life. Years later a meteor struck at Murchison (Victoria) was also analyzed and its contents found to be similar to those of the dischar

13、ge experiment of Stanley Miller,Early Energy System,The first living organisms gained their energy by a fermentation of the organic soup C6H12O6 Alcohol + CO2 + EnergyHowever there was only a limited amount of organic nutrients in the primeval soup and to sustain life. ( First Famine ). A new effici

14、ent Energy Source was required.,Role of Blue Green Algae,Blue Green Algae & Photosynthetic Bacteria developed to use water as a hydrogen donor and produced dioxygen as a by product. Photosynthesis nCO2 + nH2O ( CH2O)n + nO2 6CO2 + 6H20 C6H12O6 + 6O2,Decline of Anaerobic Bacteria,Problem for Anaerobi

15、c Organisms Evidence of the appearance of Oxygen is indicated in the (Red Layers) of the Grand Canyon. O2 is believed to have entered the atmosphere about 1.8 Billion years ago Fe2+ and oxygen reactions may have delayed entry of oxygen into the atmosphere.,Oxygen Rich Planet,Oxygen Rich Planet The b

16、uild up of Oxygen in the atmosphere led to the formation of the Ozone Layer at 15 to 60 km above the earth. Ozone O3 absorbs harmful UV light and this allowed organisms to colonize the Water/Land/ Atmosphere interface.,Oxygen Rich Planet,Respiration utilized the photosynthetic Compounds (Sugar ) to

17、produce Energy (CH2O)n + nO2 nCO2 + H2O + E This process was 18 times more efficient than the fermentation process .But oxygen can damage cellular material,The trouble with oxygen,The ultilization of oxygen in producing energy resulted in emergence Eukarotic cells which contained a nucleus which pro

18、tected cellular material prone to oxidation.( DNA),The present atmosphere,The present atmosphere has arisen from (1) The distance of the earth from the sun (2) Nature of the earths composition (3) The rise of life.,Distance from the Sun,The distance from the Sun determines the kinetic energy (KE) of

19、 the molecules in the atmosphere due to the Suns heat and the molecules velocity.KE = 1/2 mv2 & KE = 3/2kT Where m is the mass of the molecule (Mr /NA)k is the Boltzmann constant (R/NA)( Earth !50 x 106km) Transit of Venus Capt Cook to within 2% of the value 1788,Influence of Earths Mass,The ability

20、 of molecules to remain in the atmosphere is also related to the mass of the earth. The escape Velocity Ve = (2Gm/R)1/2 m = Mass, G=Universal Gravitational Constant, R = Radius,Escape Velocity,Escape Velocity (Ve) Ve = (2Gm/R)1/2 m = Mass of the PlanetG= Universal Gravitational Constant,R = Radius o

21、f the Planet Escape Velocities in km/s Earth = 11.2 Venus = 10.3 Mars = 5.0,Escape Velocity,The ability of molecules to remain in an atmosphere is related to the mass.Density Diameter Distance from SunMars 3.94g/ml 6794km 227.9 Mkm Earth 5.52g/ml 12756km 149.6 Mkm The Molecules Escape Velocity and n

22、ature of the molecules determines the composition of the atmosphere.,No H or He in Earths Atmosphere,At 600 K (Upper Atmosphere ) For H atoms 1 in 106 exceeds the escape velocity.This is High enough for rapid depletion of H from the atmosphere As a result all the Hydrogen on earth is present in a bo

23、und state.(Water, Organic material),Little CO2 in atmosphere,For Oxygen only 1 in 1084 atoms exceeds the escape velocity .This indicates negligible depletion of Oxygen. Presence of Life on Earth has removed Carbon dioxide from the Atmosphere and given rise to oxygen. Shellfish/Coral.( Calcium Carbon

24、ate and Plant Material ),Earth ,Venus & Mars,Surface Characteristics of PlanetsTemperature Pressure (bar)* Venus 732 K (459oC) 90 Earth 288 K ( 15oC ) 1 (101325Pa) Mars 223 K (-55oC ) 0.006 *1 bar = 100,000Pa= 10m in depth of the Ocean,Distribution of Gases on Earth Venus & Mars,Composition of Plane

25、ts Atmospheres in %CO2 N2 O2 SO2 H2O Venus 96.5 3.5 0.015 Earth 0.03 78.1 20.9 (varies) Mars 95.3 2.7 0.1 0.03,Role of Shellfish,Presence of Life on Earth has removed Carbon dioxide from the Atmosphere and given rise to oxygen. Shellfish/Coral. in the Sea,Air,Land Interface has immobilized Carbon di

26、oxide as Calcium Carbonate while Photosynthesis has given rise to oxygen and Plant Material,Triple point of H2O,P(H2O) in Atmospheres,Temperature K,Venus,Earth,Mars,ICE,WATER,VAPOUR,Triple Point,1,10-6,200,380,Water ( Solid,Liquid, Gas),The Surface temperature of the Earth at 1 atmosphere Pressure i

27、s close to the Triple Point for water.Water is the only compound that can exits in the environment as a Solid, Liquid and Gas simultaneously. The thermodynamic properties of Water have been essential in determining our present climate and support of life.,Super Greenhouse & Acid Rain,On Venus ,the h

28、igh level of CO2 and its distance from the Sun have lead to a super greenhouse effect and Sulphuric Acid Rain. Where the surface pressure in 90 times that of Earths ( 900 m in the Ocean)and surface temperature is about 460oC(Melting point of Zn = 419oC),Current Atmosphere,Composition of Current Atmo

29、sphere %VolN2, O2, Ar, CO2, H2O78.08 20.95 0.93 0.03 (Variable)ppm Ne He K CH418 5.2 1.1 1.25 Early Atmosphere Rich in CO2, CH4,Present Level of Oxygen,The present level of Oxygen in the atmosphere is balanced at a such a level that less would impede survival of a number of organisms while more woul

30、d lead to a greater probability of fires.At 25 % oxygen damp twigs and grass of a rain forest would ignite.,Structure of Atmosphere,Earths Atmosphere,Earths Surface,Troposphere,Stratosphere,Mesosphere,Thermosphere,REGION,10-16 km (-56oC),50 km (-2oC),85 km (-92oC),500 km (1200oC),15oC,O3,O2+, NO+,O2

31、+, O+, NO+,N2,O2,CO2,H2O,3 x 10-6 atm,0.001 atm,0.1 atm,1atm,Ozone Layer,Ozone in the Stratosphere 16 - 50km above the Earths Surfaceacts as a blanket preventing harmful radiation that can marked affect living material from reaching the surface of the Earth.,Ozone and Radiation,Oxygen that lies abov

32、e the stratosphere filters out UV light 120nm - 220nm Ozone O3. In the Stratosphere filtersout UV light 220nm - 320nm Regions UV C 200nm - 280nm UV B 280nm - 320nmUV A 320nm - 400nm ( less harm),Effects of Reduction in Ozone,(Effects of Reduction) 1% Reduction In O3 2% increase in UV-B Skin sunburns

33、, tans, Skin cancer Absorbed by DNA DNA damage Possible eye cataracts Interferes with photosynthesis Organisms in 1st 5metre of the Oceans at risk( phytoplankton in particular ),Chlorofluorocarbons & Ozone,Destruction of the Ozone Layer discovered in 1970s by CFCs ( Chlorofluorocarbons) First synthe

34、sized Swartz (1892) Used as refrigerants 1928 (Midgely & Henne) CCl4 + xHF CCl(4-x)Fx + HCl(Aerosol Propellants & Air conditioners),Ozone Protection,ProtectionO2 + h 2O.O. + O2 O3O3 + h O. + O2 ( UV-B),Ozone Destruction,Destruction CFCl3 Cl. Chlorine(UV-C, UV-B) RadicalCl. + O3 O2 + ClO.ClO. + O. Cl

35、. + O2 ClO. + ClO. ClOOCl (relatively stable),Control of CFCs,CFCs are now under strict control and their use has been curtailed.Australia signed the international treaty. “The Montreal Protocol“ in June 1988 which has a program controlling the use and reduction of CFCs.,Uses of CFCs,Compound Use CF

36、C- 11 CFCl3 Refrigeration, aerosol, foam CFC-12 CF2Cl2 sterilization, cosmetics food freezing, pressurizedblowers. CFC-113 CCl3CF3 solvent, cosmetics Halon 1301 CBrF3 fire fighting (discontinued),Lifetime of CFCs,Compound Ozone Depleting Lifetime(yrs) Potential CFC- 11 1.0 65 -75 CFC-12 1.0 100 - 14

37、0 CFC-113 0.8 100 - 134 CFC-115 0.6 500 CCl4 1.2 50 - 69 Halon 1301 10 110,Naming of CFCs,( 90 Rule) CFCs name is related to its Formula. CFC 123 123 + 90 = 213The remaining bonds are allocated to Cl or BrC = 2 , H =1 , F = 3 , Cl = ( 8 - 6) = 2CFC 123 is CF3CHCl2Letters with the number indicate an

38、isomer.,C,H,F,Chloromonoxide,Evidence for the destruction has been linked to the catalytically active Chloro monoxide ClO. & Ozone profiles as one goes South. It is interesting to note how little Chloro monoxide effects the amounts of Ozone.,Relationship between ClO. & O3,Ozone Layer,Ozone (O3),Chlo

39、rine monoxide ClO.,Chlorine monoxide ,ppb,Ozone, ppm,1.0,0,2.5,0.5,Latitude,63oS,73oS,Thickness of Ozone Layer,The thickness of the Ozone Layer is expressed in Dobson units (DU) and is equivalent to 0.001 mm thickness of pure O3 at the density it would possess at ground level (1 atm)Equator = 250 DU

40、Temperate Latitudes = 350 DUSubpolar regions = 450DU,Other Ozone Depleters,But has the reduction and removal of CFCs solved the problem of the Ozone Hole ? Or could there be other causes that are producing the Ozone Hole. ?Could our pollution arising from NO2 and CO2 contributing factors ?,Interacti

41、ve Catalytic Forms,Destruction: Halide Radicals destroy Ozone.The majority of Chlorine does not exit as Cl. or ClO The two major nonradical inactive as catalysts species in the Stratosphere are:HCl Hydrogen chloride ClONO2 Chlorine nitrate gas,Interactive Catalytic Forms,Formation of nonradical chlo

42、rine species.ClO. + NO2. ClONO2Cl. + CH4 HCl + CH3.But HCl react with Hydroxyl Radical HCl + OH. H2O + Cl.( ClO. & Cl. Catalytically Active ),Origin of Ozone Hole,The major destruction of the hole in the lower atmosphere occurs as a result of special winter weather conditions when the chlorine store

43、d as the catalytically inactive forms (HCl & ClONO2 ) are converted to the catalytically active forms (ClO. & Cl.)(This occurs in Polar Stratospheric Clouds),Ice crystal formation,Nitric acid in the atmosphere forms from the reaction between OH.& NO2. Catalytically inactive to active chlorine occurs

44、 on the surface of ice crystals formed from water and nitric acid in the lower stratosphere in winter when the temperature drops to -80oC over the South Pole.,Possible Role of CO2,“ CO2 acts as a blanket in the lower atmosphere,” says Salawitch. “ To balance the books the Stratosphere has to cool” T

45、hus CO2 could be contributing to helping PSC formation due to reduced temperatures in the stratosphere.New Scientist, 1 May 1999 p28,Impenetrable Vortex formation,The usual warming mechanism from of O + O2 O3 + Heatis absent due to total darkness and the stratosphere becomes very cold. As a result t

46、he air pressure drops ( PV=nRT ) and due to the rotation of the earth an impenetrable vortex forms with winds up to 300km/hr,PSCs,Matter cannot readily enter this vortex and the air inside is isolated and remains cold for many months. ( Mid October) The crystals formed by the condensation of the gas

47、es within the vortex formPolar Stratospheric Clouds which consist of crystals of trihydrate of Nitric Acid.,HCL attachment,Gas phase HCl attaches to the ice particle,Crystal,HNO3.3H2O,of,HCl,HCl,HCl,HCl,HCl,HCl,Ice Particle formed at low Temperature(-80oC),Role of ClONO2,Ozone Layer (Radicals in PSC

48、),Crystal,HNO3.3H2O,of,HCl,HCl,HCl,HCl,HCl,HCl,ClONO2,Cl2,ClONO2 collides with HCl to form Molecular Chlorine,Accumulatesin Winter,Formation of Cl. Radicals,Ozone Layer (Radicals in PSC),Crystal,HNO3.3H2O,of,HCl,HCl,HCl,HCl,HCl,HCl,ClONO2,Cl2,Cl.,Cl,When the Light in Summer appears Cl2 is converted to Cl.,UV light Summer,Accumulatesin Winter,Hole Closure,ClONO2(g) also reacts with water H2O(s) + ClONO2(g) HOCl(g) +HNO3(s)HOCl + UV light OH. + Cl. It is only when the vortex has vanished does chlorine predominate in its inactive forms and the hole closes.,