Abstract The properties of particulate matter PM, including its impact on the environment and human health, depend mainly on the size (more precisely: size distribution) of the particles since the size is usually dependent on the processes/sources of the PM. This work presents the results of a one-year-long measurement campaign of PM. PALAS Fidas 200 from Airpointer air quality station was used. The PM was measured in Warsaw, Poland continuously from 1st May 2022 to 30th April 2023; size distribution was recorded with 120 s intervals and averaged in 3600 s periods. It was found, that the number and the mass size distribution varied depending on the averaging period (different hours of the day, different days of the week, and different months of the year). Additionally, the authors determined the periods of impact on selected sources (traffic emission, municipal emission, and industrial emission) on the number and mass size distributions of PM at the sampling site. Monitoring of number and mass size distributions of PM is a relatively easy and more cost-effective method than analysing the chemical composition of PM. Therefore, is crucial to develop a method of identifying sources of PM based on size distributions. It was found that such a method can be in the future as successful in source apportionment as in the analysis of chemical compositions.