Association of inhaled particulate matter (PM) with adverse health effects by independent and diversified scientific work has provided the ground for revision of the PM Air Quality Standard in the U.S.A. and for the proposal of increasingly stringent daughter Directives of the Commission's Air Quality Framework Directive. The amendment of the standards sets maximum ambient mass concentration levels for particulates in different size modes. Monitoring particulate mass concentration of different sizes may lead to potential complications in environmental impact assessments and setting future emission standards for motor vehicles, because only limited information on particulate size is available now. In addition, more information on particulate characteristics is needed by medical research, in order to support the understanding of mechanisms via which combustion related particulates harm human health. Objectives: Based on the above, it is necessary to collect and analyse information regarding the characterisation of motor vehicle emitted particulates in a scientifically and technically sound manner. The characterisation should include parameters already introduced by the air quality standards (size, number concentration, etc.), but also other components (surface area, chemical composition, etc.) in order to help towards the investigation of particulate fate and provide useful input to medical studies.