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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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 (CH Mechanism4)
CH4 + 8O2→ CO2 + 2H2O + 4O3
Degradation of ethane (C Mechanism2H6)
C2H6 + 14O2→
2CO2 + 3H2O + 7O3
Unreactive product formation Mechanism
Branched chain VOC
e.g. methylpropene, t-butanol
VOC degraded in CRI v1 Mechanism
123 VOC – similar coverage of NAEI inventory as MCM (i.e. 70% of mass emissions)
Coupling with inventory VOC speciation Mechanism
NAEI speciated VOC inventory
ca. 70% coverage of mass emissions
MCM: broken line Mechanism
CRI: full line
Development of CRI v2 Mechanism
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 Mechanism
Performance of individual VOC schemes tested against MCM v3.1 (Steve Utembe)
PTM with trajectories for 31 July 1999 used for this purpose:
Simulated ozone using MCM v3.1 with NMVOC emitted entirely as a single alkane
Optimisation of CRI v2 pentane scheme as a single alkane
Cycloalkanes in NAEI speciation – all emitted as cyclohexane
CRI mechanism v2 – concluding remarks cyclohexane
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.