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Development of the Common Representative Intermediates (CRI) Mechanism

Development of the Common Representative Intermediates (CRI) Mechanism. Quantifying ozone formation from VOC degradation. Carter (1994) Maximum Incremental Reactivity (MIR) Scale ‘kinetic reactivity’ ‘mechanistic reactivity’. Derwent et al. (1998)

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Development of the Common Representative Intermediates (CRI) Mechanism

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  1. Development of the Common Representative Intermediates (CRI) Mechanism

  2. Quantifying ozone formation from VOC degradation Carter (1994) Maximum Incremental Reactivity (MIR) Scale ‘kinetic reactivity’ ‘mechanistic reactivity’ Derwent et al. (1998) Photochemical Ozone Creation Potential (POCP) Scale ‘kinetic contribution’ ‘structure-based contribution’ Stedman et al. - national ozone forecasting activities Highly parameterised chemistry ‘OH reactivity’ ‘ozone yield’

  3. Degradation of methane (CH4) CH4 + 8O2→ CO2 + 2H2O + 4O3

  4. Degradation of ethane (C2H6) C2H6 + 14O2→ 2CO2 + 3H2O + 7O3

  5. Unreactive product formation Branched chain VOC e.g. methylpropene, t-butanol unreactive products + other products e.g. acetone very slow CO, CO2

  6. VOC degraded in CRI v1 • 10 ketones (C3-C6) • 17 alcohols (C1-C6) • 10 ethers (C2-C7) • 8 esters (C2-C6) • 3 carboxylic acids (C1-C3) • 2 other oxygenates (C3) • 8 chlorocarbons (C1-C2) • 22 alkanes (C1-C12) • 15 alkenes (C2-C6) • 2 dienes (C4-C5) • 1 monoterpenes (C10) • 1 alkyne (C2) • 18 aromatics (C6-C11) • 6 aldehydes (C1-C5) 123 VOC – similar coverage of NAEI inventory as MCM (i.e. 70% of mass emissions)

  7. Coupling with inventory VOC speciation MCM v3 125 VOC 4,400 species 12,700 reactions NAEI speciated VOC inventory 650 VOC CRI v1 123 VOC 250 species 570 reactions ca. 70% coverage of mass emissions

  8. MCM: broken line CRI: full line

  9. Development of CRI v2 Objectives of ongoing work Review representation of chemistry of individual VOC classes – compensating errors ? Validate mechanism against MCM v3.1 Expand coverage to include a large number of additional alkanes, alkyl-substituted cycloalkanes and alkyl-substituted aromatics Provide chemistry of additional VOC as modular add-on to MCM

  10. CRI Mechanism Performance of individual VOC schemes tested against MCM v3.1 (Steve Utembe) PTM with trajectories for 31 July 1999 used for this purpose:

  11. Simulated ozone using MCM v3.1 with NMVOC emitted entirely as a single alkane

  12. Optimisation of CRI v2 pentane scheme

  13. Cycloalkanes in NAEI speciation – all emitted as cyclohexane

  14. CRI mechanism v2 – concluding remarks Development of CRI mechanism v2 has commenced with optimisation being performed by comparison with MCM v3.1. The treatment of individual VOC classes is being considered separately (e.g., alkanes; alkenes; aromatics). Work to date suggests that the mechanism is improved by defining separate series of intermediates for different VOC classes. This will result in an increase in size, but should allow a more rigorous description of the impact of different source sectors, and a better foundation for mechanism expansion.

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