Kraków is among the cities with the highest particulate matter levels within Europe. We conducted long-term and highly time-resolved measurements of the chemical composition of submicron particlulate matter (PM₁). Combined with advanced source apportionment techniques, which allow for time-dependent factor profiles, our results elucidate that traffic and residential heating (biomass burning and coal combustion) as well as oxygenated organic aerosol are the key PM sources in Kraków.