To date, studies on particulate matter in Hong Kong have been vastly based on filter sampling and off-line analysis, with coarse time resolution (24 to 48 h per sample) and the need for time- and material-consuming post-sampling laboratory analyses. The main objective of this work is a comprehensive real-time assessment of particulate matter composition, temporal trends in concentration on different scales (diurnal, weekly, monthly, seasonally), size distributions and source apportionment at the roadside in a typical urban city environment in Hong Kong, using an Aerodyne high-resolution time of flight aerosol mass spectrometer (HR-ToF-AMS) and additional data from collocated instruments measuring gas-phase and particle-phase species as well as metereological parameters. The results of this study will serve to better characterize important primary aerosol sources in the urban environment (particularly traffic and residential/commercial emissions) and to identify contributions of long-range transport (i.e. non-local emissions) on road-side pollution and to ultimately provide a basis for the establishment of appropriate  regulation and mitigation strategies.