Ultrafine Particles in Concern of Vehicular Exhaust—An Overview

There is a growing consensus among health experts all over the world that the particles in nano- and ultrafine range (<100 nm diameter) are having significant vulnerable effect on the human health regarding carcinogenicity and cardiovascular diseases. Worldwide experimental study on the vehicles with advanced technology, both gasoline and diesel, shows reduction in PM mass but increased particle number mainly in the ultrafine range known as the ultrafine particles (UFPs). Hence, characterization of particulates in terms of their size distribution and number is of great importance for the vehicles operating on different fuels and a wide range of technology spectrum. New emission regulations, Euro V and Euro VI implemented in Europe, which are likely to get harmonized in India, will cover only diesel and gasoline direct injection engines. UFPs are emitted from almost every fuel combustion process, including diesel, gasoline, and jet engines, as well as external combustion processes such as burning of woods, coal, and other natural phenomena like forest fires. Consequently, there is growing concern that people living in close proximity to highly trafficked roadways and other sources of combustion-related pollutants (airports and rail yards) may be exposed to significant levels of UFPs and other air toxics. This chapter covers the UFPs process of formation, physiochemical characteristics, the fate of transportation, and health impact. The last section of this chapter highlights mainly about the needs of the future research on UFPs.