Source apportionment of particle number concentrations: A global review

There are strong indications that exposure to ultrafine particles (UFP) (mobility diameters ≤100 nm) can induce adverse health effects. UFP can be present in the atmosphere through direct emissions such as from motor vehicles or through new particle formation events. To be able to develop control strategies or to provide source specific exposure metrics, it is possible to perform source apportionments using particle number size distributions. Thus, this study has searched the literature for all papers reporting source apportionments based on particle size distributions and compiled them into a database of all published studies. Typically reported sources include nucleation, several traffic sources, space heating, secondary inorganic aerosol, and particles associated with oxidants as represented by ozone. Nucleation and traffic typically dominated the particle number concentrations.