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 JenkinCentre for Environmental Policy m.jenkin@imperial.ac.uk

1993 – the conception 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

1993-2007: Master Chemical Mechanism

Philosophy

to use information on the kinetics and products of elementary reactions relevant to VOC oxidation to build up a rigorous 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 construction methodology

Mechanism construction is broadly a two-stage process:

1. Development of a “mechanism construction protocol”

2. Application of the protocol to a series of emitted (primary) VOC to develop the mechanism/database

MCM version emitted VOC species reactions protocol

v1 (1996) 102 (+18) 2,400 7,100 (1)

v2 (1999) 124 3,800 11,400 (2)

v3 (2002) 126 4,400 12,700 (3,4)

v3.1 (2004) 136 5,900 13,500 (5)

Mechanism development and protocol history

(1) Jenkin et al. (Atmos. Env. 31, 81, 1997): non-aromatic species

(2) Report on DETR contract, EPG 1/3/70 (1998) : aromatic species

(3) Saunders et al. (ACP, 3, 161, 2003): non-aromatic species

(4) Jenkin et al. (ACP, 3, 181, 2003): aromatic species

(5) Bloss et al. (ACP, 5, 641, 2005): aromatic species

123125135

MCM timelineMCM v1 - 120 VOC; 7100 reactions; 2400

species101 non-aromatic anthropogenic species18 aromatics (provisional chemistry)1 biogenic species (isoprene)

1996

MCM v2 - 123 VOC; 11400 reactions; 3800 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

MCM v3.1 - 135 VOC; 13500 reactions; 5900 species

114 non-aromatic anthropogenic species18 aromatics (updated representation)4 biogenic species (isoprene: pinene: -pinene:

MBO-232)

2004

The Master Chemical Mechanism (1993-2007)

Degradation of CH4 and 134 non-methane VOC ca. 5,900 chemical species ca. 13,500 chemical reactions

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) 3 other oxygenates (C3-C5) 17 halocarbons (C1-C3)

Species cover ca. 70% of the mass emissions in the UK National Atmospheric Emissions Inventory

(anthropogenic)

Includes isoprene, pinene, pinene and MBO-232 (biogenic)

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

Flow diagram of main features of MCM protocols

Structure of the protocols Initiation reactions

OH, NO3, O3, photolysis

Reactions of organic radicals reaction with O2

Reactions of RO2 intermediates reaction with NO, NO2, NO3, HO2 and R’O2

Reactions of RO intermediates reaction with O2, decomposition and isomerisation

Reactions of Criegee intermediates excited and stabilised

Removal of Cl atoms Reactions of degradation

products

Approximate hierarchy of information sources

1) Experimental data (evaluated)

2) Experimental data (direct)

3) SARs (published)

4) SARs/analogy assumptions (defined in protocol)

5) Theoretical studies of specific structures

Simplifications Initiation criteria Channel probability Product degradation RO2 + RO2/R’O2

VOC

carbonyl product

OH HO2

RO2 RO

NO NO2

NONO2

O2

O2 reaction,decomposition orisomerisation

Free radical propagated reaction cycle

h O3O2

h

O2O3

NO2 + h → NO + OO + O2 (+M) → O3

(+M)

VOC

carbonyl product

OH HO2

RO2 RO

NO NO2

NONO2

O2

HNO3NO2

Radical termination

H2O

2HO2

O2 reaction,decomposition orisomerisationROOH

HO2

ROH + R-

HO

RO2

NO

RONO2

NO2

RO2NO

2

VOC

carbonyl product

OH HO2

RO2 RO

NO NO2

NONO2

O2

O2 reaction,decomposition orisomerisation

Radical generation (or regeneration) through photolysis

O3

h

H2O

carbonyls

h

O2

carbonyls

hO2

ROOH h

H2O2

h

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. 4,000 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 1000 RO2 radicals in MCM

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 1000 radicals would require 0.5 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 1000 RO radicals in MCM 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 gas phase mechanism

(i.e. MCM)

Scientific and policy modelling

Fundamental

parameters

Chemical mechansim

s

Mechanism application

Reduced gas phase

mechanisms

Chamber data

Evaluation

Parameterisation

Website/ database