Exposure to ultrafine particles (diameter less than 100 nm) is an important topic in epidemiological and toxicological studies. This study used the average particle number size distribution data obtained from our measurement survey in major microenvironments, together with the people activity pattern data obtained from the Italian Human Activity Pattern Survey to estimate the tracheobronchial and alveolar dose of submicrometer particles for different population age groups in Italy. We developed a numerical methodology based on Monte Carlo method, in order to estimate the best combination from a probabilistic point of view. More than 106 different cases were analyzed according to a purpose built sub-routine and our results showed that the daily alveolar particle number and surface area deposited for all of the age groups considered was equal to 1.5 × 1011 particles and 2.5 × 1015 μm2, respectively, varying slightly for males and females living in Northern or Southern Italy. In terms of tracheobronchial deposition, the corresponding values for daily particle number and surface area for all age groups was equal to 6.5 × 1010 particles and 9.9 × 1014 μm2, respectively. Overall, the highest contributions were found to come from indoor cooking (female), working time (male) and transportation (i.e. traffic derived particles) (children).Highlights► We estimate particle number and surface area deposition for different age groups and lifestyles through an indirect approach. ► Particle number distribution range for each microenvironment was obtained from our measurement survey data. ► Deposition increases as a function age group, with the maximum value observed for 41–65 years old. ► Major contributions arise from indoor cooking and eating times (female), working time (male) and transportation (children).