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Hong Kong is a densely populated city with heavy traffic volume.A large number of volatile organic compounds（VOCs）,which are the precursors of tropospheric ozone and secondary organic aerosols（SOAs）,are emitted from traffic-related sources.Special attention has been paid on the characteristics of roadside VOCs and their impacts on the local air quality of Hong Kong during the past decades.In this study,proton transfer reaction-mass spectrometry（PTR-MS）,an advanced technique with high-temporal resolution and low detection limit,is firstly applied to the simultaneous real-time monitoring of oxygenated volatile organic compound（OVOCs） and VOCs at a roadside station in Hong Kong.The performances of PTR-MS were examined under different relative humidity and temperature of inlet air with hydronium ion（H3 O+） as the primary ion source.The sensitivity of 17 species of atmospheric significance was of insignificant humidity dependence,except for formaldehyde（m/z = 31）.The detection sensitivity of formaldehyde decreased with the increase of humidity due to the back reaction of protonated HCHO with water vapor prior to analysis,and a reverse function was found with a best-fitting curve.Strongly correlation between calibrated reaction rate,inlet relative humidity and temperature was found which matched well by poly-2 D regression.Formaldehyde is the most variable specie when the inlet relative humidity and temperature are changed.The accuracy and precision of the measurements were less than 15%.Inter-comparison were also performed between the measurement from PTR-MS,off-line DNPH cartridge samples and on-line GC-FID system.Formaldehyde,acetaldehyde,acetone,MEK,benzene,toluene,C8-aromatics showed good correlation between PTR-MS and alternative sampling methods.Our results suggested that PTR-MS can be applied on the long term measurements of roadside VOCs and OVOCs with good stability and reliability in Hong Kong.