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O
O
OO
OO
OO
OO
O
O
O
O
O
OH
OO
O
O
OO
-pinene
pinonic acidpinonaldehyde
O
OO
stab.
O
OHO
acetone andother products
stab. 0%
OO
+ H2O
O
+ H2O
OO
50%
O
OHO
OH
87.5%12.5%
45%
- OH
- OH
60%40%
50%- OH- CO
+ O2
20%
55% + O2
80%
O
O
O
C9 acyl-oxy radical
formaldehydeO
OOO
RO2 or HO2 + O2
decomp.+ O2
O
O
decomp.
OH
- CO2
decomp.
OO
decomp.
isom.
pinic acid
+ O2
acetone, formaldehyde and other products
isom.
+ O2
+ O2 decomp.
20%O
O
OH
10-hydroxy-pinonic acid
OH80%RO2 or HO2
RO2
RO2
H2O2H2O
O3O3
OO
O
O
OH
O
OH
OO
OH
OO
OH
O
OH+ HO2
OHO
O
OHO
O
OO
OH
O
O
OHO
O
O
OH
O
O
O
O
O
O
O
O
O
OOO
OO
O
O
O
+ HO2+ HO2 + HO2
+ HO2
+ HO2
+ HO2
nitrate
nitrate
nitrate
H abstraction OH addition
1,4 addition1,2 addition
O2
O2
O2
O2
O2
NO
NO
NONO
NO
NO
O2
9.0%
16.0%
1.0%
1.0%
9.0%
24.7%7.0% 7.0%
21.0%
4.3%
'phenolic'
'peroxide-bicyclic'
'epoxy-oxy'
O2O2
O2
isom.
isom.
decomp.
decomp.decomp.
decomp.
History of the Master Chemical Mechanism
(MCM) and its development protocols
Mike JenkinEPSR GroupDepartment of Environmental Science and Technology [email protected]
1993 – the birth of the MCM
University of Leeds Sam Saunders, Mike Pilling AEA Technology Mike Jenkin, Colin Johnson UK Meteorological Office Dick Derwent
Work commissioned by the Department of the Environment, DoE (Air Quality Division), to improve the treatment of organic chemistry in ozone policy models
Chemical processing of ozone-precursor emissions
VOC NOX
CO2
H2O
nitrate
emissions
oxidation
Ozoneinventory contains ca. 650 species
Chemistry in DoE ozone models in 1993
Photochemical Trajectory Model
chemistry of 95 VOC represented
although reasonably detailed, the chemistry did not reflect the current status of kinetic and mechanistic data, e.g.
- no formation of organic nitrates from RO2 + NO
- RO2 + HO2 reactions not included (except for CH3O2)
- incomplete degradation of some VOC
- many VOC degraded via products known to be wrong (i.e. incorrect RO reactions applied)
- very limited representation of photolysis of organics
1993-1996: Master Chemical Mechanism (MCM v1)
Philosophy
to use information on the kinetics and products of elementary reactions relevant to VOC oxidation to build up an explicit representation of the degradation mechanisms. the resultant formation of ozone and other gas-phase
secondary pollutants
apply measured and evaluated parameters (e.g. rate coefficients; branching ratios) from the literature where possible.
use analogy and ‘structure-reactivity correlations’ to define the other reactions and parameters.
‘Mechanism Development Protocol’- Atmospheric Environment, 31, 81-104, 1997
1996: Master Chemical Mechanism (MCM v1)
Degradation of CH4 and 119 non-methane VOC ca. 2,500 chemical species ca. 7,000 chemical reactions
22 alkanes (C1-C12) 16 alkenes (C2-C6) 2 dienes (C4-C5) 1 alkyne (C2) 18 aromatics (C6-C11) 6 aldehydes (C1-C5)
10 ketones (C3-C6) 17 alcohols (C1-C6) 10 ethers (C2-C7) 8 esters (C2-C6) 3 carboxylic acids (C1-
C3) 8 halocarbons (C1-C3)
MCM website launched in March 1997
MCM timeline
MCM v1 - 120 VOC; 7000 reactions; 2500 species
101 non-aromatic anthropogenic species18 aromatics (provisional chemistry)1 biogenic species (isoprene)
1996
MCM v2 - 123 VOC; 10500 reactions; 3500 species
103 non-aromatic anthropogenic species18 aromatics (extended provisional chemistry)2 biogenic species (isoprene: pinene)
1999
MCM v3 - 125 VOC; 12700 reactions; 4400 species
104 non-aromatic anthropogenic species18 aromatics (first rigorous representation)3 biogenic species (isoprene: pinene: -pinene)
2002
Contributions to MCM v2 and v3 activities at Leeds:Nic Carslaw, Stephen Pascoe, Volker Wagner
2002: Master Chemical Mechanism (MCM v3)
22 alkanes (C1-C12) 16 alkenes (C2-C6) 2 dienes (C4-C5) 2 monoterpenes (C10) 1 alkyne (C2) 18 aromatics (C6-C11) 6 aldehydes (C1-C5)
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 halocarbons (C1-C3)Supplementary protocols:
•Atmospheric Chemistry and Physics, 3, 161-180, 2003 (non-aromatic VOC)
•Atmospheric Chemistry and Physics, 3, 181-193, 2003 (aromatic VOC)
O
O
OO
OO
OO
OO
O
O
O
O
O
OH
OO
O
O
OO
-pinene
pinonic acidpinonaldehyde
O
OO
stab.
O
OHO
acetone andother products
stab. 0%
OO
+ H2O
O
+ H2O
OO
50%
O
OHO
OH
87.5%12.5%
45%
- OH
- OH
60%40%
50%- OH- CO
+ O2
20%
55% + O2
80%
O
O
O
C9 acyl-oxy radical
formaldehydeO
OOO
RO2 or HO2 + O2
decomp.+ O2
O
O
decomp.
OH
- CO2
decomp.
OO
decomp.
isom.
pinic acid
+ O2
acetone, formaldehyde and other products
isom.
+ O2
+ O2 decomp.
20%O
O
OH
10-hydroxy-pinonic acid
OH80%RO2 or HO2
RO2
RO2
H2O2H2O
O3O3
OO
O
O
OH
O
OH
OO
OH
OO
OH
O
OH+ HO2
OHO
O
OHO
O
OO
OH
O
O
OHO
O
O
OH
O
O
O
O
O
O
O
O
O
OOO
OO
O
O
O
+ HO2+ HO2 + HO2
+ HO2
+ HO2
+ HO2
nitrate
nitrate
nitrate
H abstraction OH addition
1,4 addition1,2 addition
O2
O2
O2
O2
O2
NO
NO
NONO
NO
NO
O2
9.0%
16.0%
1.0%
1.0%
9.0%
24.7%7.0% 7.0%
21.0%
4.3%
'phenolic'
'peroxide-bicyclic'
'epoxy-oxy'
O2O2
O2
isom.
isom.
decomp.
decomp.decomp.
decomp.
MCM construction methodology
MCM scheme writing framework
Free radical propagated oxidation cycle
VOC
carbonyl product(s)
OH HO2
RO2 RO
NO NO2
NONO2
O2
rxn with O2,decomposition orisomerisation.
h O3O2
h
O2O3
NO2 + h → NO + OO + O2 (+M) → O3
(+M)
Radical termination
VOC
carbonyl product(s)
OH HO2
RO2 RO
NO NO2
NONO2
O2
HNO3NO2
H2O
2HO2
ROOH
HO2
ROH + R-
HO
RO2
NO
RONO2
rxn with O2,decomposition orisomerisation.NO
2
RO2NO
2
Radical generation (or regeneration) through photolysis
VOC
carbonyl product(s)
OH HO2
RO2 RO
NO NO2
NONO2
O2
H2O2
ROOHcarbonyls RONO2
rxn with O2,decomposition orisomerisation.
ROOH carbonyls
O3
O2
O2H2
O
organic compound
first generation products
CO2
second generation products
ozone
organicaerosol
OHRO2
RO HO2
NONO2 NO NO2
OHRO2
RO HO2
NONO2 NO NO2ozone
ozone
sunlight
sunlight
sunlight
h h
h
h
CH4
HCHO
CO
CO2
OH
HO2
CH3O2
CH3O
OH
HO2
HCO
OH
HO2
HOCO
NO NO
NO
NO NO2
NO2
NO2 NO2 O3O3
O3
O3
C
H
HH
H
OH-initiated degradation of methane (CH4)
OH HO2C2H6
NO NO2
NONO2
CH3CHOC2H5O
CH3C(O)O2
CH3C(O)O
CH3O2
HO2
OH
CH3O
CO2HCHO
NO
NO2
NONO2
NO
NO2
HCO
OHHO2
CO
NO NO2
OH
HO2
HOCO
NO
NO2
CO2
O2O2
O2
O2O2O2
O2
C2H5O2H2O
H2O
H2OOH-initiated degradation of ethane (C2H6)
C C
HH
H HH H
OH-initiated degradation of 1,3-butadiene
OHO
OOHO
OHO
OHOO
HO
HO
O
OO
O
O
HO
O
OO
O
O
O
OOHO
O
OHO
OHO
OH
OO
OHO
OH
O
O
O
NO2
OH
HO2
OH
NO NONO2 NO2
HO2 OH
NO NONO2
NO
HO2
OH
HO2
HCO
OH
HO2
NO2NO
HOCO
NO2
OH
CO2
HCHO
CO
NO
NO
NO
NO
CO2
NO2
HO2
NO
NO NO2
NO2 NO2
HO2
OH
NO
NO
NO
OH
HO2
OH
HOCH2CO3
NO
NO2
NO2
NO2
HOCH2CO2
HOCH2CHO
NO2
NO2
NO2
HO2
HCHO
CO2
OH
HO2
HCO NO NO2
C C
H
H
C
H
C
H H
H
Defining kinetic and mechanistic parameters
VOCor
product
carbonyl product(s)
OH
HO2
RO2 RO
NO NO2
NONO2
O2
rxn with O2,decomposition orisomerisation
• OH + VOC/organic product
• RO2 + NO, NO2, NO3, HO2, R’O2
• RO O2 reaction, decomp., isom.
OH radical reactions
Kinetics of OH + VOC/organic products Rate coefficients have been measured for several hundred
organics Rate coefficients for ca. 2,000 species need to be estimated
(e.g. SAR method of Atkinson, 1994; Kwok and Atkinson, 1995)
Product radical distribution of OH + VOC/organic product Mainly inferred from SAR partial rate coefficients Scheme simplification measures applied in some cases
- minor channels (<5%) ignored
- single representative channel for ≥ C7 alkanes
- so called ‘minor’ products (e.g. RONO2; ROOH) degraded to regenerate existing species
RO2 radical reactions Kinetics of RO2 reactions
Reactions with NO, NO2, NO3, HO2 and other peroxy radicals (R’O2) are included in MCM
There are about 1200 RO2 radicals in MCM v3
Kinetic data are available for only ca. 20 RO2 – parameters assigned to majority of reactions by analogy and structure reactivity correlations
Product branching ratios Multiple channels for reactions with NO, HO2 and R’O2
Scheme simplification measures applied in some cases
- RO2 from ‘minor’ products react via single channel
- RO2 + R’O2 reaction are necessarily parameterised (explicit chemistry for 1200 radicals would require 0.7 million reactions!)
RO radical reactions
reaction with O2R R'
O
R R'
O+ O2 + HO2
R R'
O
R+ R'
O
R
O
R'R
OH
R'
decomposition
isomerisation
There are about 1200 RO radicals in MCM v3 Relative importance of these modes of reaction largely defined by
SAR methods of Carter and Atkinson (1989) and Atkinson (1997)
Simplification measure
oxygenated RO radicals – exclusive
decomposition assumed
R
O
OR + CO2
R'
acyl-oxy
R
O
-hydroxy-oxy
-carbonyl-oxy
O
R'
-alkoxy-oxy
R
OR'
O
R
OH
O
R'R
OHR'
O
RO
O
RO
O
R'
VOC/product initiation reactions
Reaction with OH – all VOC and oxygenated products
Reaction with O3 – alkenes/dienes and unsaturated products
Reaction with NO3 – alkenes/dienes, aldehydes and cresols
Photolysis – carbonyls, RONO2, ROOH
Carbonyls
HCHO HCO + H (J11) 4.642 x 10-5 0.762 0.353 CO + H2 (J12) 6.853 x 10-5 0.477 0.323
CH3CHO HCO + CH3 (J13) 7.344 x 10-6 1.202 0.417
C2H5CHO HCO + C2H5 (J14) 2.879 x 10-5 1.067 0.358
n-C3H7CHO HCO + n-C3H7 (J15) b 2.792 x 10-5 0.805 0.338
CH3CHO + C2H4 (J16) 1.675 x 10-5 0.805 0.338
i-C3H7CHO HCO + i-C3H7 (J17) b 7.914 x 10-5 0.764 0.364
CH2=C(CH3)CHO CH3C=CH2 + HCO (J18) b 1.140 x 10-5 0.396 0.298
CH2=C(CH3)CO + H (J19) b 1.140 x 10-5 0.396 0.298
CH3C(O)CH3 CH3CO + CH3 (J21) 7.992 x 10-7 1.578 0.271
CH3C(O)C2H5 CH3CO + C2H5 (J22) b 5.804 x 10-6 1.092 0.377
CH3C(O)CH=CH2 CH3CH=CH2 + CO (J23) 1.836 x 10-5 0.395 0.296 CH3CO + CH=CH2 (J24)
b 1.836 x 10-5 0.395 0.296
-Dicarbonyls
(CHO)2 CO + CO + H2 (J31) 6.845 x 10-5 0.130 0.201 CO + HCHO (J32) 1.032 x 10-5 0.130 0.201 HCO + HCO (J33) 3.802 x 10-5 0.644 0.312
CH3C(O)CHO CH3CO + HCO (J34) b 1.537 x 10-4 0.170 0.208
CH3C(O)C(O)CH3 CH3CO + CH3CO (J35) b 3.326 x 10-4 0.148 0.215
Hydroperoxides
CH3OOH CH3O + OH (J41) b 7.649 x 10-6 0.682 0.279
Organic nitrates
CH3ONO2 CH3O + NO2 (J51) 1.588 x 10-6 1.154 0.318
C2H5ONO2 C2H5O + NO2 (J52) 1.907 x 10-6 1.244 0.335
n-C3H7ONO2 n-C3H7O + NO2 (J53) b 2.485 x 10-6 1.196 0.328
i-C3H7ONO2 i-C3H7O + NO2 (J54) b 4.095 x 10-6 1.111 0.316
t-C4H9ONO2 t-C4H9O + NO2 (J55) b 1.135 x 10-5 0.974 0.309
CH3C(O)CH2ONO2 CH3C(O)CH2O + NO2 (J56) b 7.549 x 10-6 1.015 0.324
CH3CO + HCHO + NO2 (J57) b 3.363 x 10-6 1.296 0.322
Organic photolysis processes
•26 photolysis processes defined
•14 parameters also used to define photolysis rates for several thousand other species
• Laboratory studies
• Theoretical and semi-empirical
methods
e.g.
rate coefficients, branching ratios,
absorption spectra, quantum yields
• Detailed mechanism construction
(MCM) • Scientific and policy modelling
Fundamental
parameters
Mechanism developme
nt
Mechanism application
• Mechanism reduction
Chamber validation