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

School of Chemistry Toluene Oxidation Routes in MCMv3.1 Little ring opening along phenol route Successive addition of OH, NO 3. Leads to formation of nitrophenols Low ozone formation route Ring opening routes are most active photochemically and dominate ozone formation

School of Chemistry Design of chamber experiments: ozone isopleth construction

School of Chemistry 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 O 3 - NO 2 is not rapidly enough - Co-products of glyoxal/ Me glyoxal not detected in sufficient conc n

School of Chemistry  -dicarbonyls. Photolysis (NO = 0) and ‘photosmog’ experiments (with NO)(Cork, Valencia measurements) photolysis photosmog

School of Chemistry Butenedial: MCMv3.1 photolysis mechanism vs photolysis observations

School of Chemistry 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. CH 3 CO + O 2 → CH 3 CO 3 * → OH + CH 2 CO 2 CH 3 CO 3 * + M → CH 3 CO 3 Can such routes operate in aromatic chemistry?

School of Chemistry EXACT-1 : Attempts to improve the model performance by including an NO 2 aerosol sink /HONO source and an early source of OH Alternative mechanisms are also feasible,e.g. Volkamer, O3 + furanones

School of Chemistry 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 O 3 formation – need route to radical formation that doesn’t give NO to NO 2 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  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 HO 2 formation O 3 +  -dicarbonyls / furanones Improved detection methods for glyoxal co-products