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Testing and developing aromatic mechanisms against EUPHORE chamber data

Mike Pilling, University of Leeds MCM Workshop, Leeds, January18th, 2007. Testing and developing aromatic mechanisms against EUPHORE chamber data. Toluene Oxidation Routes in MCMv3.1. Low ozone formation route. Little ring opening along phenol route Successive addition of OH,

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Testing and developing aromatic mechanisms against EUPHORE chamber data

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  1. Mike Pilling, University of Leeds MCM Workshop, Leeds, January18th, 2007 Testing and developing aromatic mechanisms against EUPHORE chamber data

  2. Toluene Oxidation Routes in MCMv3.1 Low ozone formation route Little ring opening along phenol route Successive addition of OH, NO3. Leads to formation of nitrophenols Ring opening routes are most active photochemically and dominate ozone formation

  3. Design of chamber experiments: ozone isopleth construction

  4. Comparison of MCM3.1 to Toluene Chamber Experiment (27/09/01) • Conclusions: • - Ozone overpredicted • but OH is too low. Need • early OH source that • doesn’t produce O3 • NO2 is notrapidly • enough • - Co-products of glyoxal/ • Me glyoxal not detected • in sufficient concn

  5. g-dicarbonyls. Photolysis (NO = 0) and ‘photosmog’ experiments (with NO)(Cork, Valencia measurements) photolysis photosmog

  6. Butenedial: MCMv3.1 photolysis mechanism vs photolysis observations

  7. Searching for an OH production route • Alkyl peroxy radicals isomerise / dissociate to from OH only at high T • Modification of the peroxy can lead to low T production of OH: • e.g. • CH3CO + O2 → CH3CO3* → OH + CH2CO2 • CH3CO3* + M → CH3CO3 • Can such routes operate in aromatic chemistry?

  8. EXACT-1 : Attempts to improve the model performance by including an NO2 aerosol sink /HONO source and an early source of OH Alternative mechanisms are also feasible,e.g. Volkamer, O3 + furanones

  9. Current status of aromatic mechanisms • Mechanism underestimates total radical production rates by a factor of ~2 at short and long times. • At the same time, mechanism overestimates O3 formation – need route to radical formation that doesn’t give NO to NO2 conversion. • NOx removed from system more rapidly than mechanism indicates • Coproducts of glyoxal and Meglyoxal from toluene not fully characterised • Photochemistry and photosmog experiments on g dicarbonyls are incompatible in terms of radical yields – need new chemistry. • Further extensive experiments on other aromatics – benzene, p-xylene, 1,3,5 trimethyl benzene, hydroxy aromatics, using both EUPHORE and small chambers for kinetics. Provide detailed mechanistic and kinetic data, but problems remain. • Need new detailed experiments, e.g. by laser flash photolysis or discharge flow on targeted intermediates: • OH and HO2 formation • O3 + g-dicarbonyls / furanones • Improved detection methods for glyoxal co-products

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