Chapters%203%20and%20part%20of%204

Chapters%203%20and%20part%20of%204 - -Pollution formation...

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Env. Chemistry, Baird & Cann -Pollution formation -Detrimental effects of pollution (outdoor & indoor) animals, plants, and materials of polluted air -Methods for combating air pollution -Detailed reactions that occur in clean and polluted air are discussed in Chapter 5.
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The atmosphere is divided into several regions
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Oxidizing Environment (O 2 ) in the Troposphere Pollutants are eventually oxidized –the air is cleansed
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Chemical Fate of Trace Gases in Clean Air Most gases in the atmosphere (Table 2-1) are oxidized but none react directly with oxygen; the reactions begin with hydroxyl radical Hydroxyl radicals are the vacuum cleaner of the troposphere Lifetime is only about a second and concentration is very small; concentration drops quickly to 0 at night
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Env. Chemistry, Baird & Cann
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Formation of Hydroxyl Radicals O 3 O 2 O H 2 O O 2OH * * * + + . UV-B
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Destruction of Methane CH 4 + 2O 2 CO 2 + 2 H 2 O Catalyzed by OH Details of the pathway or mechanism of this reaction will be later in the chapter 5 OH catalyst
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The Origin and Occurrence of Smog Smog (combination of sm oke and f og ) induced by light Primary pollutants Secondary pollutants VOCs +NO . +O 2 sunlight O 3 +HNO 3 +organics VOCs (including uncombusted hydrocarbons and natural sources) + NO from cars and trucks The most reactive hydrocarbons are alkenes VOCs – Volatile Organic Compounds –
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Smog Formation (cont.) Internal combustion engine (fig 2-1) N 2 +O 2 flame 2NO air oxidation 2NO 2 NO produced from air nitrogen is called thermal NO ; from nitrogen in the fuel is called fuel NO High E act
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Figure 2-1
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Mixture of NO and NO2 that imparts a yellow hue (fig 2-2) to smog and is know as NO x Conditions for photochemical smog Vehicular traffic Sunlight Little air movement
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Thermal Nitric Oxide O 2 2O equilibrium K eq = [O] 2 /[O 2 ] O + N 2 NO + N Slow rate determining step Rate = K 2 [O][N 2 ] = K 2 [N 2 ](K eq /[O 2 ]) 1/2 Rate = K’[N 2 ][O 2 ] 1/2
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Oxidation of NO 2 NO + O 2 2NO 2 Nitrogen Dioxide NO and NO 2 together are referred to as NOx NOx can develop from the oxidation of thermal and fuel NO and from natural sources (lightning and biological activity through the oxidation of ammonia
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Formation of Ground Level Ozone Like the stratosphere ozone is produced by reaction of an O atom with O 2 NO 2 NO + O O + O 2 O 3 Major source of O atoms is photochemical decomposition of NO 2 which come from slow oxidation of NO from vehicles 2NO air oxidation 2NO 2 Complex reaction that takes hours and involves free radical catalysts UV-A
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Smog Formation NO from vehicles (large populations)
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Chapters%203%20and%20part%20of%204 - -Pollution formation...

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