In order to support risk management in identifying effective mitigation measures, exposure assessment related to environmental pollution needs to integrate monitoring of pollution levels and control data with information on population behaviour and lifestyle. With this aim, a sample population survey was carried out in a Northern Italian city, collecting data on human behavioural factors influencing inhalation exposure. Questionnaires gathering data on dwelling characteristics, and weekly individual diaries on personal behaviour, such as places frequented and daily activities, were used. Data collection was carried out in two different seasons, spring-summer and fall-winter. A sample of 270 families, randomly selected from the municipal registry, was enrolled for each seasonal observation. The study allowed quantification of variability in human behaviour revealing seasonal variation and differences due to age and gender. Daily activity patterns were described and probability distributions of inhalation rates were obtained for all observed population groups. A probabilistic exposure model was developed and the resulting exposure distributions for the two seasonal periods were compared. Results confirm that exposure estimates are strongly biased if variability in human behaviour is not taken into account.