Andrew Rickard, Claire Bloss, Mike Jenkin, Sam Saunders and Mike Pilling

1. University of Leeds Department of Chemistry Gas phase MCM development Andrew Rickard, Claire Bloss, Mike Jenkin, Sam Saunders and Mike Pilling

2. Overview • Update to MCMv3.1 • Aromatic chemistry • New schemes (MBO) • Development of new schemes (MOST) • Ethylene glycol di-vinyl ether (DVE-1) • Ethylene glycol mono-vinyl ether (MVE-1) • MOST EUPHORE 2005 photo-smog experiments • Future Work • Update of photolysis rate parameters • Future scheme developments (open for discussion) • UWA (Hong Kong/ Australian emissions) – Chloro-benzenes • Biogenics (Terpenes) • cyclohexanes/cycloalkenes

3. Development of MCMv3.1 - Aromatics • Total aromatics form a significant fraction of anthropogenic VOC – from vehicle emissions and solvent use • Highly reactive compounds with high emissions – substantial contribution to ozone formation • Degradation schemes for 4 aromatics (benzene, toluene, p-xylene and 1,3,5-trimenthylbenzene) have been updated on the basis of new kinetic and mechanistic data • Performance of these mechanisms evaluated using detailed photo smog chamber data from the EU EXACT campaigns Heavily instrumented 200 m3teflon foil chamber Long path FTIR – aromatic parent compound, O3, HCHO, HNO3 UV absorption – O3 ; DOAS – NO2, glyoxal Chemiluminescence – NO ; LIF – OH, HO2 Filter radiometer – J(NO2) GC techniques, HPLC, CO monitor

4. Development of MCMv3.1 - EXACT • EXACT database contains photochemical smog chamber studies on all four mono-aromatics. • Other experiments on specific key areas of aromatic oxidation, focusing on subsets of the toluene system. • Where appropriate, results from EXACT have been used to refine the mechanisms. • This development work on mono-aromatics has been extended to update the degradation schemes of the 12 other mono-aromatics with saturated alkyl side chains in MCMv3.1.

5. MCMv3.1 – Update of Aromatics • Key areas in which the aromatic mechanisms have changed are: • Lower benzaldehyde yield in the toluene system. • Updated photolysis rates of unsaturated γ–dicarbonyls (ring opening products). • Breakdown of (5H)-furan-2-one (photolysis product of butenedial) has been updated and β–angelica lactone has been replaced by α–angelica lactone to reduce secondary glyoxal formation. • New phenol-type chemistry has been implemented reflecting lower yield for ring opening channel and need for reduced ozone formation from evaluation against EXACT/EUPHORE cresol smog chamber experiments. • Primary aromatic oxidation branching ratios have been adjusted to reflect new reported yields of glyoxal and phenol type compounds (under atmospheric conditions).

6. MCMv3.1 – Toluene Oxidation

7. MCMv3.1 – EXACTCresol Oxidation • Peak O3 is well simulated with MCMv3.1 • Representation of NO and NO2 profiles is improved • However, radical yield is too low as rate of cresol oxidation is underestimated • Results from comparison with EXACT cresol experiments used to adjust hydroxyarene degradation in MCMv3.1 • In MCM3.1a first generation ring retained products are treated in the same way as the original cresol

8. MCMv3.1 – EXACT Butenedial Oxidation • Faster removal due to increased photolysis rate in MCMv3.1 • However, OH and HO2 are much lower than measured • NOxy chemistry poorly understood • Secondary peak due to formation of PAN • Ozone simulated well (coincidence?!)

9. MCMv3.1 – EXACT Benzene Oxidation • O3 peak again greatly reduced using MCMv3.1 • Good agreement due to increase in phenol yield • However, increase in ring-retaining products leads to a decrease in oxidising capacity of the system (OH better simulated using MCMv3) • This is indicative of the general mechanistic problem: • Over prediction of O3 but under prediction of the system reactivity.

10. MCMv3.1 – EXACTToluene Oxidation • O3 peak still greatly overestimated using MCMv3.1 • increased branching for ring open products (early) • increased photolysis of unsat. dicarbonyls (early) • changes in phenol chemistry decreases O3 formation in middle of experiment • higher “missing” OH for MCMv3.1 • Reduced oxidative capacity consistent with reduced O3 formation potential

11. MCMv3.1 – Update of Aromatics • In general MCMv3.1 shows improved ability to simulate some of the EXACT observations and represents our current understanding of aromatic degradation. • However, significant discrepancies remain concerning ozone formation potential and oxidative capacity of aromatic hydrocarbon systems: • Peak O3 is simulated well for benzene but over estimated for the substituted aromatics. • OH radical production is too low to account for the OH inferred from the rate of loss of the parent aromatic. • For a majority of the systems the NO oxidation rate is under predicted. This parameter is linked to the production of O3 and the oxidative capacity of the system. • Ideas and strategies for resolving these issues have been suggested and additional laboratory and smog chamber experiments are required in order to investigate them further.

12. MCMv3.1 – Other updates • New scheme for biogenic hydrocarbon MBO (2-methyl-3-buten-2-ol) added with 93 new reactions, 30 new species All major new products already in MCM • Extended list of chloro- and hydrochlorocarbons and 2 hydrobromocarbons • MCMv3.1 now contains 135 primary emitted VOCs • c.a. 5600 species and 13500 reactions

13. Mechanism Development – MOST • Multiphase chemistry of Oxygenated Species in the Troposphere

14. Mechanism Development – MOST • Multiphase chemistry of Oxygenated Species in the Troposphere • Organic solvents are used in a large number of industrial processes and due to their volatility many are emitted either directly or indirectly into the atmosphere. • A number of organic compounds employed as solvents at the present time have been shown to have adverse health effects, carcinogenic, mutagenic and reprotoxic properties • Solvents also undergo complex chemical reactions in the atmosphere, which lead to the formation of compounds which are environmentally damaging, in particular the formation of photochemical oxidants • It is now well accepted that the switch from additional solvents to oxygenated compounds is inevitable both in terms of toxicity problems and in order to reduce the levels of oxidant formation in the troposphere • The solvent industry within Europe has targeted a limited range of ethers, ketones, esters and glycols as replacements for traditional solvents

15. MOST – Key Oxygenates

16. MOST EUPHORE 2005 - Proposal • “To Carry out carefully designed chamber experiments involving the measurement of reactants, intermediates and products in the presence of NOx under conditions which simulate ambient tropospheric conditions (NOx and VOC limited)” • (c.f. EXACT 2001-2002) • These experiments will build upon/bring together what we have learned from the MOST chamber studies 2002/2003

17. MOST EUPHORE 2005 – Model Compounds • Experiments to be carried out with model compounds • short chain to suppress isomerisation • symmetrical • known products (easy to calibrate, can we measure them easily?) • simplify chemistry • separate experiment(s) focussing on important intermediates (eg. formates)? • Chosen models: • DVE-1 • (Ethylene glycol di-vinyl ether) • Vinyl ether model • Aerosol formation (OH and O3) • MVE-1 • (Ethylene glycol mono-vinyl ether) • Vinyl alcohol model • Aerosol formation (OH and O3)

18. Explicit mechanism construction • Approaches: • Construction “by hand” following MCM protocol. • MECHGEN automatic generation using expert systems techniques used as an initialisation tool. • Problems: • MECHGEN does not allow for use of experimental values, only SARs are used. • Implemented SARs/GRs may not be appropriate for these oxygenated species. • SARs: Kwok and Atkinson, Atmos. Env., 29, 1685 (1995). • Peeters et al., Chemosphere, 38, 1189, (1999). • GR: Porter et al., J. Phys. Chem. A., 101, 5770 (1997).

19. Mechanistic Detail – DVE-1 + OH • Rate constant estimated by analogy

20. DVE-1– degradation scheme 1 (OH) kOH = 8.77E-11 (SAR) = 8.52E-11 (GR) = 16.7E-11 (AN) 332 OH initiated reactions

21. DVE-1– degradation scheme 2 (OH)

22. Mechanistic Detail – DVE-1 + O3 • Rate constant estimated by analogy kDVE-1+O3 = [2((2.0 + 2.4)/2)] × 10-16= 4.4 × 10-16 cm3 molecule-1 s-1 • Rate constant measured on 27/5/04 at EUPHORE: kDVE-1+O3 = 2.5 (± 0.3) × 10-16 cm3 molecule-1 s-1

23. DVE-1– degradation scheme 1(O3)

24. DVE-1– degradation scheme 2(O3)

25. MVE-1– degradation scheme (OH) 319 reactions including OH, O3 and NO3 Products HCHO (100%) ETOHOCHO? kOH = 1.03E-10 (RR) latest = 1.20E-10 (RR) = 6.4E-11 (RR) = 4.67E-11 (GR) = 4.80E-11 (SAR)

26. MVE-1– degradation scheme (O3) kO3 = 1.8 (± 0.7) E-16 latest

27. Isopleth Plots Maximum O3 formation as a function of initial NO and VOC concentrations in simulated chamber experiments. • Identify initial conditions for VOC limited and NOx limited regimes. • Used to choose conditions for chamber experiments on aromatic compounds (EXACT).

28. Future Work Update of Photolysis Reactions

29. Update of Photolysis Reactions (1) • Photolysis rates for a core number of reactions (as a function of SZA) have been determined using a two stream isotropic scattering model (on 1st July at 0.5 km, lat. 45oN). • Variation of j with SZA is described well by the following expression: • j = l (cosX)mexp(-n.secX) • Some of these parameters are then used to define the photolysis rate of a large number of related species. • However, the laboratory measured cross sections and quantum yields for these core reactions have not been updated since 1997 and new measurements have also have become available.

30. Update of Photolysis Reactions (2)

31. Update of Photolysis Reactions (3) • j-(HOCH2CHO) chamber • cs – Atkinson et al. (2002) • qy – Atkinson et al. (2002) • j-(n-C3H7CHO)(j<15>) MCM • cs – Roberts and Fajer (1989) • qy – Atkinson et al. (1992) • j-(HCHO_R) chamber • cs – Atkinson et al. (2002) • qy – Atkinson et al. (2002) • j-(HCHO_R)(j<15>) MCM • cs – DeMore et al. (1994) • qy – DeMore et al. (1994)

32. Update of Photolysis Reactions (4) • MCM photolysis rate parameters need to be recalculated using up to date spectroscopic and photochemical information. • A thorough literature review is currently underway • New calculations will be carried out using the discrete ordinate radiative transfer models TUV(www.acd.ucar.edu/TUV)and PHOTOL (Jenkin et al. 1997b).

33. Future Work New Reaction Schemes

34. Future Scheme Development • What to do next? • Biogenics – Terpenes (sequiterpenes) • Cyclohexanes • Cycloalkenes • Chloro-benzenes (Hong Kong and China emissions)

35. Cyclohexanes: NAEI Speciation

36. Building a Hong Kong (HK) Photochemical model

37. Hong Kong Data Set • Air monitoring network data available for > 5 years, includes standard MET, NOx, Ozone, CO, SO2, TEOM PM10 and PM2.5, VOC (>200) • Beginning analysis of datasets to characterise air masses for high pollutant events e.g. measured O3 on 9th June 2004 in excess of 200 ppb • Identify significant VOC currently not included in the MCM, to enable construction of a HK photochemical model • Work initiated 1 Dec 2004, with masters student from HK Polytechnic University

38. Hong Kong Data Set • Emissions and monitoring

39. Identified missing VOC species • HK Monitoring data • > 100 compounds • 18 halo-compounds • 10 aromatic • 9 halo-aromatic • 38 HC’s • (mostly higher alkanes, alkenes, cyclo-alkanes and cyclo-alkenes) • 2 carbonyl compounds • Current MCM species • 135 VOC

40. Suggested VOC for expansion of MCM • New project initiatives require VOC scheme expansion • Some expansion work begun • Chlorobenzene • 1,5-pentanedial • Other species identified • Key VOC for HK model work • Biogenics; 1,8-cineole, d-limonene • DMS, DMDS

41. Some possible candidates identified from various emissions inventories • Alkylcyclohexanes • 3-heptanone • Ethyl hexanal • Other chlorobenzenes • 1-methyl 4-isopropyl benzene • 3-methylbenzaldehyde • Propyne • Acrolein, vinyl acetate, crotonaldehyde – to be further expanded as primary VOC (currently secondary species)