Reducing Air Pollution In Los Angeles

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Gas Phase PhotochemistryVOC NOx h? ? O3
Gail Tonnesen WRAP RMC Training
January 17, 2002
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Table of Contents

• Photochemistry Review
• Model Evaluation
• Observational Based Methods
• Chemical Process Analysis
• Photochemical Indicators
• Conclusions

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VOC is oxidized in the atmosphere OH
VOC O3 olefins carbonyls NO3 olefins
carbonyls h? carbonyls The oxidation
products of VOC react with NO to produce NO2 and
O3.
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Family Definitions NOx NO NO2
NO NO2 ( NO3 2 N2O5 HONO HNO4 ) NOz
HNO3 RNO3 NO3 PAN NOy NOx NOz
total oxidized nitrogen. organics VOC (or
ROG, NMOC, NMHC, PROC) Ox O3 NO2 NOz O
2 NO3 3 N2O5 HNO4 HOx OH HO2 RO2
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Fundamental Photochemistry

• Tropospheric gas phase chemistry is driven by the
  OH radical
• Radical Initiation
• Radical Propagation
• Radical Termination
• NOx termination

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Photo Stationary State Equilibrium
NO2 h? ? NO O O O2 ?
O3 O3 NO ? O2 NO2 P(Ox) RO2 NO ?
RO NO2
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Radical Initiation
O3 h? ? O(1)D O(1)D H2O ? 2
OH HCHO h? ? 2 HO2 CO HO2 NO ?
OH NO2 HONO h? ? OH NO PAN ? RO3
NO2
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Radical Propagation
OH CH4 O2 ? CH3 O2 H2O CH3O2 NO ?
NO2 CH3O CH3O O2 ? HO2 HCHO
HO2 NO ? NO2 OH 2x( NO2 h? O2 ? O3
NO ) Net Reaction CH4 4 O2 ? 2 O3 HCHO
H2O
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Radical and NOx termination
OH NO2 ? HNO3 HO2 HO2 ? H2O2 HO2
RO2 ? ROOH RO2 NO? RNO3 RO3 NO2?
PAN N2O5 H2O ? 2 HNO3
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Photochemical Mechanisms

• Master Chemical Mechanism
• 12000 reaction, 5000 species
• 123 VOC represent 97 of mass.
• Carbon Bond IV (CB4, CB4-99, CBMZ)
• lumped carbon bonds, 7 VOC
• RADM2, RACM2
• lumped molecules, 10 VOC, detailed RO2 chemistry
• SAPRC 10 VOC, detailed RO2 chemistry.
• Morphecules (Jeffries, Kessler and Gery)

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Model Evaluation

• Verification, Validation or Evaluation?
• Oreskes et al., Science, 1994.
• Compare state variables with ambient data
• Validation of component processes.
• Use indicators for testing O3 sensitivity.
• Sensitivity and uncertainty analysis.