History of the Master Chemical Mechanism MCM and

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 l University of Leeds Sam Saunders, Mike Pilling l AEA Technology Mike Jenkin, Colin Johnson l UK Meteorological Office Dick Derwent l Work commissioned by the Department of the Environment, Do. E (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 CO 2 H 2 O nitrate

Chemistry in Do. E ozone models in 1993 Photochemical Trajectory Model l l 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 RO 2 + NO - RO 2 + HO 2 reactions not included (except for CH 3 O 2) - 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 v 1) Philosophy l l l 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 v 1) l l l Degradation of CH 4 and 119 non-methane VOC ca. 2, 500 chemical species ca. 7, 000 chemical reactions l l l 22 alkanes (C 1 -C 12) 16 alkenes (C 2 -C 6) 2 dienes (C 4 -C 5) 1 alkyne (C 2) 18 aromatics (C 6 -C 11) 6 aldehydes (C 1 -C 5) l l l 10 ketones (C 3 -C 6) 17 alcohols (C 1 -C 6) 10 ethers (C 2 -C 7) 8 esters (C 2 -C 6) 3 carboxylic acids (C 1 -C 3) 8 halocarbons (C 1 -C 3) MCM website launched in March 1997

MCM timeline 1996 MCM v 1 - 120 VOC; 7000 reactions; 2500 species 1999 MCM v 2 - 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 v 3 - 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 v 2 and v 3 activities at Leeds: Nic Carslaw, Stephen Pascoe, Volker Wagner

2002: Master Chemical Mechanism (MCM v 3) l l l l 22 alkanes (C 1 -C 12) 16 alkenes (C 2 -C 6) 2 dienes (C 4 -C 5) 2 monoterpenes (C 10) 1 alkyne (C 2) 18 aromatics (C 6 -C 11) 6 aldehydes (C 1 -C 5) l l l l 10 ketones (C 3 -C 6) 17 alcohols (C 1 -C 6) 10 ethers (C 2 -C 7) 8 esters (C 2 -C 6) 3 carboxylic acids (C 1 -C 3) 2 other oxygenates (C 3) 8 halocarbons (C 1 -C 3) 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 O 3 hu O 2 NO 2 VOC O 2 NO OH HO 2 RO O 2 O 3 NO NO 2 hu carbonyl product(s) rxn with O 2, decomposition or isomerisation. NO 2 + hu → NO + O 2 (+M) → O 3 (+M)

Radical termination HNO 3 H 2 O 2 NO 2 VOC O 2 ROOH HO 2 RO HO 2 RO 2 NO NO NO 2 ROH + R-HO RO 2 NO 2 carbonyl product(s) rxn with O 2, decomposition or isomerisation.

Radical generation (or regeneration) through photolysis ROOH H 2 O 2 O 3 NO 2 H 2 O VOC O 2 carbonyls O 2 NO OH HO 2 RO O 2 carbonyls NO NO 2 ROOH carbonyl product(s) rxn with O 2, decomposition or isomerisation. RONO 2

OH-initiated degradation of methane (CH 4)

OH-initiated degradation of ethane (C 2 H 6)

OH-initiated degradation of 1, 3 -butadiene

Defining kinetic and mechanistic parameters NO 2 VOC or product O 2 NO OH HO 2 RO NO NO 2 carbonyl product(s) rxn with O 2, decomposition or isomerisation • OH + VOC/organic product • RO 2 + NO, NO 2, NO 3, HO 2, R’O 2 • RO O 2 reaction, decomp. , isom.

OH radical reactions Kinetics of OH + VOC/organic products l l 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 l Mainly inferred from SAR partial rate coefficients l Scheme simplification measures applied in some cases - minor channels (<5%) ignored - single representative channel for ≥ C 7 alkanes - so called ‘minor’ products (e. g. RONO 2; ROOH) degraded to regenerate existing species

RO 2 radical reactions Kinetics of RO 2 reactions l l l Reactions with NO, NO 2, NO 3, HO 2 and other peroxy radicals (R’O 2) are included in MCM There about 1200 RO 2 radicals in MCM v 3 Kinetic data are available for only ca. 20 RO 2 – parameters assigned to majority of reactions by analogy and structure reactivity correlations Product branching ratios l Multiple channels for reactions with NO, HO 2 and R’O 2 l Scheme simplification measures applied in some cases - RO 2 from ‘minor’ products react via single channel - RO 2 + R’O 2 reaction are necessarily parameterised (explicit chemistry for 1200 radicals would require 0. 7 million reactions!)

RO radical reactions reaction with O 2 decomposition isomerisation l l There about 1200 RO radicals in MCM v 3 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

VOC/product initiation reactions l Reaction with OH – all VOC and oxygenated products l Reaction with O 3 – alkenes/dienes and unsaturated products l Reaction with NO 3 – alkenes/dienes, aldehydes and cresols l Photolysis – carbonyls, RONO 2, ROOH

Organic photolysis processes • 26 photolysis processes defined • 14 parameters also used to define photolysis rates for several thousand other species

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