Anthropogenic particulate matter with sizes smaller than 1 μm (PM1) is a concerning air pollutant that can affect human health. In this study, we present PM1 measurements performed in a small town in northern Finland that is exposed to contrasting sources (residential wood burning, traffic, industrial activities). The study was conducted in winter 2021, with a mobile laboratory equipped with sophisticated on-line aerosol instrumentation. The results showed a significant increase in particulate mass and number concentrations from biomass burning in residential areas and town centre due to the high share of residences using biomass burning. Organics and equivalent black carbon (eBC) clearly dominated the PM1 composition during the highest pollution levels, followed by inorganics (sulfate, nitrate and ammonium). PAHs and a few elements (e.g. K, Cl, Zn) were as well higher during evening. A source apportionment confirmed the association between high PM1 values and biomass burning, even though the traffic contribution was also important. PM1 measurements at an industrial area showed an increase in sulfate, organics, eBC, and a few elements (e.g. Cl, Na, Fe), and characteristic size distributions. Simultaneous measurements of lung deposited surface area (LDSA) of particles showed the source-specificity of biomass burning, traffic and industrial emissions on LSDA size distributions. Overall, the results enlighten the impact of relevant pollution sources on Nordic towns air quality during the coldest months and show the importance to also consider the chemical composition, particle numbers, and LDSA in future air quality metrics.