Atmospheric particulate matter (PM) is a complex mixture of microscopic particles with different shapes, sizes and chemical compositions. The ultrafine size fraction of PM consists of particles with diameters less than 100nm. In urban areas, traffic is a dominant source of ultrafine particles (UFP). Gasoline-powered and diesel-powered engines emit UFP with different size distributions and chemical compositions. This paper describes the UFP and supporting data provided by Southern Ontario Centre for Atmospheric Aerosol Research for the purposes of identifying particle size distributions emitted from diesel-powered and gasoline-powered vehicles.