Proton-transfer-reaction mass spectrometry PTR-MS is a useful tool in ambient trace gas analysis, especially for the analysis of oxygenated volatile organic compounds OVOC. Many OVOCs are produced during photooxidation of volatile organic compounds and contribute to both the gas phase and secondary organic aerosols SOA. The inlet system of the PTR-MS instrument was modified to allow also for the measurement of the particulate phase of an aerosol with a high time resolution. The new inlet consists mainly of a denuder to strip off the gas phase, and a heater 120/150 degrees C to vaporize the aerosol particles. This inlet system was tested with pinonic acid particles generated with a nebulizer and SOA particles formed during the photooxidation of 1,3,5-trimethylbenzene and alpha-pinene with NOx in a smog chamber. The performance of this new technique is discussed and the partitioning coefficients for the oxidation products are estimated.