Ambient nano and ultrafine particles from motor vehicle emissions: Characteristics, ambient processing and implications on human exposure

The aim of this work was to review and synthesize the existing knowledge on ultrafine particles in the air with a specific focus on those originating due to vehicles emissions. As the first step, the review considered instrumental approaches used for UF particle monitoring and the differences in the outcomes they provide. This was followed by a discussion on the emission levels of UF particles and their characteristics as a function of vehicle technology, fuel used and after-treatment devices applied. Specific focus was devoted to secondary particle formation in urban environments resulting from semi volatile precursors emitted by the vehicles. The review discussed temporal and spatial variation in UF particle concentrations, as well as particle chemical composition and relation with gaseous pollutants. Finally, the review attempted to quantify the differences between UF particle concentrations in different environments. These, as well as other aspects of UF characteristics and dynamics in the air, were discussed in the context of human exposure and epidemiological studies as well as in relation to management and control of the particles in vehicle-affected environments.