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ESM202Lecture_Air_2008

ESM202Lecture_Air_2008 - ESM 202 Air Quality Reactive...

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    ESM 202 Air Quality
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  2 Reactive Atmosphere High energy environment Lots of oxidants (O 2 , O 3 , H 2 O 2 ) Hydroxyl radical (HO . ) produced by  photolysis of water:         H 2 O                     HO .  + H         H 2 O + h ν              HO .  + H very short life but very reactive light
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  3 Reactive Atmosphere OH .  also formed by photolysis of  ozone:             O 3  + h ν                  O *  + O 2   O *  + H 2 O                 2 HO . Radical oxidation reactions   CH 4  + HO               . CH 3  + H 2 O  RH + HO                . R   + H 2 O
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  4 Ozone Formation Molecular oxygen can be split by very  high energy light (high UV light):          O 2  + h ν            O + O Atomic oxygen can react with  molecular, but a “third” body is needed:         O 2  + O + M        O 3  + M
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  5 Ozone Formation
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  6 Ozone Formation Maximum natural ozone concentration  occurs in stratosphere at 20-40 km About 350,000 metric tons of ozone  formed and destroyed every day Maximum concentration levels are ~ 10  ppm Ozone is only a very small fraction of the  gases in stratosphere The actual thickness of the ozone layer is  only a few mm!
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    UV Absorption
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  8 Ozone Formation Ozone absorbs radiation in the region of  220-330 nm (UV-B) Only UV-A radiation (320-440 nm)  penetrates into the lower troposphere Absorbed energy is eventually  converted into heat Most of energy absorption is in upper  stratosphere hotter than the lower stratosphere
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