Ultrafine Particles Deposition Inside Passenger Vehicles

Although commuting time typically accounts for only 6% of the day for Americans, it has become a significant source of exposure to ultrafine particles (d(p) < 0.1 mu m) from vehicular emissions. Particle deposition onto surfaces, as an important particle loss mechanism, has been studied extensively in the indoor environments. However since air velocities, surface area to volume ratios and other contributing factors differ greatly between indoor and in-cabin environments, conclusions from indoor studies may not be directly applied to in-cabin microenvironments. In this study, ultrafine particle deposition rates were characterized under a range of air velocities and surface areas conditions inside different types of passenger vehicles. A diesel generator was used as a particle source and a Scanning Mobility Particle Sizer (SMPS) was used to measure ultrafine particle size distribution inside the test vehicles. As in-cabin air velocities increased from natural convection (<0.02 m s(-1)) to 0.65 m s(-1), ultrafine particle deposition rates increased with the greatest increases occurred for smaller particles. Other influencing factors, such as the number of passengers inside the vehicle, were also considered and investigated. It was found that ultrafine particle deposition rates are proportional to the surface areas inside vehicles consistent with previous indoor studies. Compared with available ultrafine particle deposition rates reported in the indoor environments, the in-cabin ultrafine particle deposition rates found in this study are about 3 to 20 times greater. This is likely due to higher air velocities and larger surface area to volume ratios in the in-cabin microenvironment.