Inhalation of particulate matter (PM) has been extensively associated with the worsening and onset of cardiorespiratory diseases, being responsible for millions of deaths annually. Assessment of PM deposition in the human respiratory tract is critical to better understand the health risks from environmental exposure of vulnerable age groups. In this study, PM_2.5 and PM₁₀ day-night monitoring campaigns during the cold season were carried out in Bragança, Portugal. The multiple-path particle dosimetry (MPPD) model was used to quantify total and regional depositions in the human respiratory tract for four different age groups: infant (3 months), child (9 years), adult (21 years) and elderly (65 years). The results showed that concentrations for both PM fractions were higher during the night, a period marked by the burning of biomass for residential heating. Regional deposition fractions (DF) for PM_2.5 were in the ranges 17–38% (head), 4–14% (tracheobronchial) and 20–28% (pulmonary), while for PM₁₀ were 24–67% (head), 4–27% (tracheobronchial) and 12–22% (pulmonary). Children and the elderly were found to be the most vulnerable groups to PM deposition, especially for the TB and H regions, respectively. The lifetime cancer and non-cancer risks associated with exposure to PM_2.5 exceeded the recommended limits, especially for children <10 years old. These findings provide useful information to alert authorities to the need to take action to reduce the pollution burden and protect the health, in particular of those most susceptible. Graphical