History of the Master Chemical
Mechanism (MCM) and its
development protocols
Mike Jenkin
EPSR Group
Department of Environmental Science
and Technology
m.jenkin@imperial.ac.uk
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
inventory contains
ca. 650 species
VOC
NOX
emissions
Ozone
oxidation
CO2
H2O
nitrate
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
1996
MCM v1 - 120 VOC; 7000 reactions; 2500 species
1999
MCM v2 - 123 VOC; 10500 reactions; 3500 species
101 non-aromatic anthropogenic species
18 aromatics (provisional chemistry)
1 biogenic species (isoprene)
103 non-aromatic anthropogenic species
18 aromatics (extended provisional chemistry)
2 biogenic species (isoprene: apinene)
2002
MCM v3 - 125 VOC; 12700 reactions; 4400 species
104 non-aromatic anthropogenic species
18 aromatics (first rigorous representation)
3 biogenic species (isoprene: apinene: b-pinene)
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)
MCM construction
methodology
MCM scheme writing framework
Free radical propagated oxidation cycle
O3
hu
O2
NO2
VOC
O2
NO
OH
HO2
RO2
RO
O2
O3
NO
NO2
hu
carbonyl
product(s)
rxn with O2,
decomposition or
isomerisation.
NO2 + hu → NO + O
O + O2 (+M) → O3 (+M)
Radical termination
HNO3
H2O2
NO2
NO2
VOC
O2
ROOH
HO2
OH
HO2
RO2
RO
HO2
RO2
NO
NO2 NO
NO
NO2
RONO2
ROH + R-HO RO2NO2
carbonyl
product(s)
rxn with O2,
decomposition or
isomerisation.
Radical generation (or regeneration) through
photolysis
ROOH
H2O2
O3
NO2
H2 O
VOC
O2
carbonyls
O2
NO
OH
HO2
RO2
RO
O2
carbonyls
NO
NO2
ROOH
carbonyl
product(s)
rxn with O2,
decomposition or
isomerisation.
RONO2
organic compound
sunlight
ozone
NO2
RO2
OH
NO
RO
NO
NO2
HO2
first generation products
sunlight
ozone
NO2
RO2
OH
NO
RO
NO
NO2
HO2
second generation products
ozone
sunlight
CO2
organic
aeroso
CH4
H
C
H
H
H
O3
OH
CH3O2
hu
NO2
NO
NO
CH3O
hu
NO2
HO2
O3
HCHO
OH
HCO
OH-initiated
degradation of
methane (CH4)
hu
NO2
NO
HO2
O3
CO
OH
HOCO
NO
HO2
CO2
hu
NO2
O3
NO2
NO
OH
C2H6
HO2
O2
H
H
C
C2H5O
NO
H2O
NO2
O2
C
H
H
H
C2H5O2
H2O
CH3CHO
O2
H
NO
OH
NO2
HO2
CH3C(O)O2
NO
NO2
OH
NO2
NO
HO2
OH-initiated
degradation of
ethane (C2H6)
HCHO
HCO
O2
H2O
CH3C(O)O
O2
O2
CH3O
CH3O2
CO
NO2
OH
HOCO
NO2
O2
NO
HO2
CO2
NO
CO2
OH
HO
OO
OH
HO
H
H
NO2
NO
H
C
NO2
NO
HO2
C
NO
HO
NO2
O
HO
OO
OH
NO2
HO2
O
OH
OO
NO2
NO
NO
NO
NO2
HO
OH
O
C
H
C
H
O
HO2
O
H
O
NO
O
O
NO
HO2
OH
OO
NO2
HCHO
OH
NO
NO
O
HO
OO
NO2
OH-initiated
degradation of
1,3-butadiene
O
HO
HO2
O
NO2
NO2
OH
HCO
NO2
NO
OO
O
HO
OH
OH
HO2
NO2
NO
NO
O
O
HO
HO2
OH
CO
CO2
HCHO
OH
HOCO
NO
HOCH2CHO
CO2
NO2
NO2
NO
NO
HOCH2CO2
CO2
O
NO
HO2
NO2
HO2
O
OH
HCO
OH
HOCH2CO3
HO2
NO2
NO2
Defining kinetic and mechanistic parameters
NO2
VOC
or
product
O2
NO
OH
HO2
RO2
RO
NO
NO2
carbonyl
product(s)
rxn with O2,
decomposition or
isomerisation
• 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 O2
O
R
O
+ O2
+ HO2
R'
R
O
decomposition
R'
O
+ R'
R
R'
R
OH
O
isomerisation
R'
R


R'
R
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)
acyl-oxy
O
R
R + CO2
O
a-carbonyl-oxy
O
O
R'
R
R'
R
O
O
b-hydroxy-oxy
OH
OH
R'
R
R'
R
O
O
a-alkoxy-oxy
R
O
R'
O
R
O
R'
O
Simplification measure
oxygenated RO radicals –
exclusive decomposition
assumed
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
Organic photolysis processes
Carbonyls
HCHO
 HCO + H
 CO + H2
(J11)
(J12)
4.642 x 10-5
6.853 x 10-5
0.762
0.477
0.353
0.323
CH3CHO
 HCO + CH3
(J13)
7.344 x 10-6
1.202
0.417
C2H5CHO
 HCO + C2H5
(J14)
-5
n-C3H7CHO
1.067
0.358
 HCO + n-C3H7
 CH3CHO + C2H4
(J15)
(J16)
b
2.879 x 10
-5
2.792 x 10
1.675 x 10-5
0.805
0.805
0.338
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
 CH2=C(CH3)CO + H
b
(J18)
(J19) b
-5
1.140 x 10
1.140 x 10-5
0.396
0.396
0.298
0.298
CH3C(O)CH3
 CH3CO + CH3
(J21)
7.992 x 10-7
CH3C(O)C2H5
 CH3CO + C2H5
(J22) b
5.804 x 10-6
1.092
0.377
CH3C(O)CH=CH2
 CH3CH=CH2 + CO
 CH3CO + CH=CH2
(J23)
(J24) b
1.836 x 10-5
1.836 x 10-5
0.395
0.395
0.296
0.296
 CO + CO + H2
 CO + HCHO
 HCO + HCO
(J31)
(J32)
(J33)
CH3C(O)CHO
 CH3CO + HCO
(J34) b
•14 parameters also used to
6.845
x 10
0.130
0.201
define
photolysis
rates for several
1.032 x 10
0.130
0.201
3.802 x 10
0.644
0.312
thousand
other
species
1.537 x 10
0.170
0.208
CH3C(O)C(O)CH3
Hydroperoxides
 CH3CO + CH3CO
(J35) b
3.326 x 10-4
0.148
0.215
CH3OOH
Organic nitrates
 CH3O + OH
(J41) b
7.649 x 10-6
0.682
0.279
CH3ONO2
 CH3O + NO2
(J51)
1.588 x 10-6
1.154
0.318
C2H5ONO2
 C2H5O + NO2
(J52)
-6
1.244
0.335
n-C3H7ONO2
 n-C3H7O + NO2
-6
1.196
0.328
i-C3H7ONO2
 i-C3H7O + NO2
-6
1.111
0.316
t-C4H9ONO2
-5
1.135 x 10
0.974
0.309
CH3C(O)CH2ONO2
7.549 x 10-6
3.363 x 10-6
1.015
1.296
0.324
0.322
a-Dicarbonyls
(CHO)2
•26 photolysis
processes defined
1.578
0.271
-5
-5
-5
-4
1.907 x 10
(J53)
b
(J54)
b
 t-C4H9O + NO2
(J55)
b
 CH3C(O)CH2O + NO2
 CH3CO + HCHO + NO2
(J56) b
(J57) b
2.485 x 10
4.095 x 10
Chamber
validation
• Laboratory
studies
• Theoretical and
semi-empirical
methods
e.g.
• Detailed
mechanism
construction
(MCM)
rate coefficients,
branching ratios,
absorption spectra,
quantum yields
• Scientific and
policy
modelling
• Mechanism
reduction
Fundamental
parameters
Mechanism
development
Mechanism
application