Analysis of high mass resolution PTR-TOF mass spectra from 1,3,5-trimethylbenzene (TMB) environmental chamber experiments

Abstract

A series of 1,3,5-trimethylbenzene (TMB) photo-oxidation experiments was performed in the 27-m 3 Paul Scherrer Institute environmental chamber under various NO x conditions. A University of Innsbruck prototype high resolution Proton Transfer Reaction Time-of-Flight Mass Spectrometer (PTR-TOF) was used for measurements of gas and particulate phase organics. The gas phase mass spectrum displayed ∼200 ion signals during the TMB photo-oxidation experiments. Molecular formulas C mH nN oO p were determined and ion signals were separated and grouped according to their C, O and N numbers. This allowed to determine the time evolution of the O:C ratio and of the average carbon oxidation state OS C of the reaction mixture. Both quantities were compared with master chemical mechanism (MCMv3.1) simulations. The O:C ratio in the particle phase was about twice the O:C ratio in the gas phase. Average carbon oxidation states of secondary organic aerosol (SOA) samples OS SOAC were in the range of-0.34 to-0.31, in agreement with expected average carbon oxidation states of fresh SOA (OS C =-0.5-0). © 2012 Author(s).