1Institute of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria
2Ionicon Analytik Gesellschaft m.b.H, Innsbruck, Austria
3Paul Scherrer Institut, Villigen, Switzerland
*current address: DBFZ Deutsches BiomasseForschungsZentrum gemeinnützige GmbH, Leipzig, Germany
**current address: Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA
****current address: NILU – Norwegian Institute of Air Research, Kjeller, Norway
Abstract. A series of 1,3,5-trimethylbenzene (TMB) photo-oxidation experiments was performed in the 27-m3 Paul Scherrer Institute environmental chamber under various NOx 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 CmHnNoOp 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 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 CSOA were in the range of −0.34 to −0.31, in agreement with expected average carbon oxidation states of fresh SOA ( C = −0.5–0).