Particles from internal combustion engines - what we need to know

Internal combustion (IC) engines are a major contributor to the total particulate emissions inventory, especially in urban areas. Recent epidemiological studies suggesting links between fine particles and negative health effects have sparked an increased interest in this subject. While particulate emissions from IC engines have been the focus of research for many years, a great deal of information crucial to our understanding of this subject still remains unknown. In this paper the authors address some of these unknowns, focusing primarily on the process and consequences of aerosol dilution strategy. The thermodynamics of dilution are considered, and the inadequacy of conventional constant-volume sampling dilution tunnels for ultrafine particle characterization are demonstrated using experimental data. Finally, time-resolved data demonstrating the variation in concentration of pollutants in a vehicle moving in traffic are used as an example of the difficulties in setting legislation aimed at controlling exposure to ultrafine particles.