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Development of the Common Representative Intermediates (CRI) Mechanism

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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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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’


Degradation of methane (CH4)

CH4 + 8O2→ CO2 + 2H2O + 4O3


Degradation of ethane (C2H6)

C2H6 + 14O2→

2CO2 + 3H2O + 7O3


Unreactive product formation

Branched chain VOC

e.g. methylpropene, t-butanol

unreactive products


other products

e.g. acetone

very slow



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)


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


MCM: broken line

CRI: full line


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


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:


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.