Fast evolution of urban ultrafine particles: Implications for deposition doses in the human respiratory system

► Traffic aerosol evolves within few seconds, for the formation of nucleation particles and tens of seconds for their removal. ► Close to vehicular exhausts, the respiratory exposure may be represented by a sequence of short-term high peak exposures. ► To estimate such brief exposures, measurement time resolution should be in the time scale of few tens of seconds. ► UFP respiratory doses were calculated with 1 and 0.03 Hz aerosol data, in a downtown area close to traffic. ► Differences between the two data-sets, in terms of number of UFPs deposited for each respiratory act, are discussed.