Gas phase precursors to anthropogenic secondary organic aerosol: using the Master Chemical Mechanism to probe detailed observations of 1,3,5-trimethylbenzene photo-oxidation

A detailed gas-phase photochemical chamber box model incorporating the Master Chemical Mechanism (MCMv3 1) degradation scheme for the model anthropogenic aromatic compound 1 3 5-trimethylbenzene has been used to simulate data measured during a series of aerosol chamber experiments in order to evaluate the mechanism under a variety of VOC/NO x conditionsThe chamber model was used in the interpretation of comprehensive high (mass and time) resolution measurements of 1 3 5-trimethylbenzene and its photo-oxidation products recorded by a Chemical Ionisation Reaction Time-of-Flight Mass Spectrometer (CIR-TOF-MS) Supporting gas and aerosol measurements have also enabled us to explore the missing link between the gas and aerosol phases Model-measurement comparisons have been used to gain insight into the complex array of oxygenated products formed including the peroxide bicyclic ring opening products (alpha beta-unsaturated-gamma-dicarbonyls and furanones) and the O2-bridged peroxide bicyclic ring-retaining products To our knowledge this is the first time such high molecular weight species corresponding to various peroxide bicyclic products represented in the MCMv3 1 have been observed in the gas-phase The model was also used to give insight into which gas-phase species were participating in SOA formation with the primary and secondary peroxide products formed primarily under low NOx conditions identified as likely candidates