Series07AtmosphericChemistry

Series07AtmosphericChemistry - Clouds are the Earths...

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Clouds are the Earth’s Blanket VII-1
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The Chemistry of Stratospheric Ozone Depletion • Chemistry and Photochemistry in the Stratosphere • The Antarctic Ozone Hole • Molecular Beam/Laser Spectroscopic Studies of Photochemistry VII-2
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Nations meet in Montreal to discuss global agreement on banning CFC chemicals, not usually done except for chemical warfare ageints. CFC's are in everyone's home already, so they're not killing anyone right now. Rush Limbaugh says it's a fraud, a scientific consipracy, grant grubbing, and government just interfering with our lives. What's going on? An otherwise arcane area of chemistry catapulted into international prominence. A combination of lab measurements, satellite data, plane flights, and physical chemistry is needed to piece the puzzle together of why ozone is being lost. Ozone in the News VII-3
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A Problem with No National Boundaries Air Conditioner Repair Man Arizona says CFC’s are OK CFC’s smuggled in from Mexico, which also OK’s CFC’s VII-4
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The Ozone Shield Less than 0.5% of Earth’s Radius; Protects all life on earth VII-5
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Temperature Profle in the Atmosphere Troposphere T decreases with increasing altitude; Adiabatic cooling as density gets lower Minimum defnes tropopause Stratosphere T increases with increasing altitude; Due to absorption oF sunlight by ozone ±rom 15-60 km VII-6
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O 2 , Dioxygen Octet on each atom Stable Ozone, O 3 Non-octet O=O O-O=O 21% of atmosphere 4 times weaker bond Reactive and caustic . . • • • • • • VII-7
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Ozone Absorption Spectrum Absorbs light between 220 and 300 nm N 2 and O 2 do not absorb at those wavelengths Protects DNA from UV light and damage VII-8
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Chapman Cycle: 1930’s Light absorption breaks the O-O bond in ozone Forms O In presence of a third body, forms O 3 again Does NOT explain ozone hole Ozone Destruction Ozone Formation . VII-9
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Concentration of Species in the Atmosphere Water and Ozone are highest, by far Others are small, but they don’t have 8 electrons! VII-10
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Total Pressure: 20-200 Torr H 2 O 1-10 ppm O 3 1-10 ppm ClO 0.1-3 ppb BrO 1 ppt O 1 ppt-1ppb Cl 0.1 ppt-10 ppt Little Things Mean a Lot VII-11
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Molecule with odd number of electrons “Open Shell” Typically highly reactive Some atmospheric radicals Cl, Br H O ClO OH NO BrO O 2 H Free Radicals : Cl : O . VII-12
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Propagation (by each Cl atom) Termination (example) One photon can lead to 10 n reactions Cl 2 + h ν Cl + Cl Cl + CH 4 HCl + CH 3 CH 3 + Cl 2 CH 3 Cl + Cl Etc., etc…. .until Cl + Cl Cl 2 or Cl + CH 3 CH 3 Cl . Radical Chain Reactions
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This note was uploaded on 10/27/2010 for the course CH 1a taught by Professor Lewis during the Fall '08 term at Caltech.

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Series07AtmosphericChemistry - Clouds are the Earths...

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