Size-resolved particle number and volume emission factors for on-road gasoline and diesel motor vehicles

Average particle number concentrations and size distributions from ∼61,000 light-duty (LD) vehicles and ∼2500 medium-duty (MD) and heavy-duty (HD) trucks were measured during the summer of 2006 in a San Francisco Bay area traffic tunnel. One of the traffic bores contained only LD vehicles, and the other contained mixed traffic, allowing pollutants to be apportioned between LD vehicles and diesel trucks. Particle number emission factors (particle diameter Dp>3nm) were found to be (3.9±1.4)×1014 and (3.3±1.3)×1015 # kg−1 fuel burned for LD vehicles and diesel trucks, respectively. Size distribution measurements showed that diesel trucks emitted at least an order of magnitude more particles for all measured sizes (10