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Wk 4b Ch 6 VOCs & oxidants

Wk 4b Ch 6 VOCs & oxidants - Chemistry of the...

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Chemistry of the Troposphere several slides donated by: Mitchio Okumura California Institute of Technology
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Photochemical Photochemical Smog Smog RH + OH R• + H 2 O R• + O 2 + M RO 2 + M RO 2 + NO RO• + NO 2 NO 2 + hv NO + O O + O 2 + M O 3 + M + particles!
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Photochemical Formation of Ozone in the Lower Troposphere RH + OH R• + H 2 O R• + O 2 + M RO 2 + M RO 2 + NO RO• + NO 2 NO 2 + hv NO + O O + O 2 + M O 3 + M Hydrocarbons Light Ingredients of SMOG
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Smog in Los Angeles, 1943 Aliso St. Butadiene Plant
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Stage I Smog Alerts in LA 1976-2001
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US EPA
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1-hour Average Peak Concentration 0-60 ppb 61-79 ppb 80-99 ppb 100-110 ppb 111-124 ppb 125+ ppb
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Ohio 1- hour Ozone Avg. 1-hour Average Peak Concentration 0-60 ppb 61-79 ppb 80-99 ppb 100-110 ppb 111-124 ppb 125+ ppb
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The New Smog Winner: Houston, Texas The Houston Ship Channel is the largest petrochemical processing complexes in the US. Hydrocarbon releases, especially ethene, propene, etc, lead directly to the high ozone levels in the US
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China Regionwide dispersal of Haze Beijing UN studies show that the worst (?) air pollution is in cities within the Third World, such as China, Mexico. Winds can transport aerosols, ozone, as well and NOx rich air over wide areas SeaWiFS satellite
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Key Problems Enough atmospheric measurements to form an up-to-date data base Chemistry for Modeling Rate constants, products Pressure, Temperature, Humidity dependences Wide variety of species Structure-Activity Relationships Reaction Mechanisms Transient Intermediates Many possible pathways Large # unobserved Role of Adducts Weakly Bound Species (BDE < 25 kcal/mol) undetected Transient complexes pressure effects Heterogeneous reactions, aerosol formation…
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Rate and Mechanisms of Gas-Phase Reactions in Irradiated Organic-NOx-Air Mixtures BJFP/JNP book: Chapter 6 In troposphere ( 30 years of study) Many types of organics Alkanes, alkenes, alkynes, aldehydes, carboxylic acids Oxidizing species OH O 3 NO 3 HO 2 Cl
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Tropospheric Oxidants OH and O 3 (hydroxyl radical & ozone) Most important oxidants for trop. organics NO 3 (nitrate radical) Nighttime oxidant HO 2 (hydroperoxyl radical) Does not directly play a large oxidative role rapid reverse reactions Cl (atomic chlorine / radical) Important in marine areas all sources have not been identified
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