This paper presents a 120-day-long variability of chemical composition of submicron particulate matter (PM 1 ) over Warsaw. The content of the following components was examined in the PM 1 mass: primary (POM) and secondary (SOM) organic matter, secondary inorganic matter (SIM), elemental carbon (EC) as well as Na and Cl ions (primary inorganic matter). The 24-hour concentrations of PM 1 were subject to seasonal fluctuations which are typical of urban areas in Poland; their values averaged 11 µg

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... m -3 in summer and 17 µg m -3 in winter. Most of the PM 1 components and gaseous pollutants (SO 2 , NO 2 and NO x ) revealed higher mean concentrations in winter than in summer. A statistical analysis of meteorological parameters and 24-h concentrations of PM 1 , PM 10 , SO 2 , NO 2 and NO x confirmed a significant influence of air temperature and precipitation on the concentration patterns of these pollutants over Warsaw. The highest concentrations of PM 1 occurred in winter for the following wind directions: S, SE, N and NE; in summer for NE, E and S. The analysis of back trajectories demonstrated that on days with the highest 24-h concentration of PM 1 polluted air masses arrived from S and SE and affected the concentration of PM 1 over Warsaw. The submicron particulate matter, in as much as 62%, comprises secondary matter (SOM and SIM). The primary sources of its precursors and -to a smaller extent -of the primary matter as well -are traffic and combustion of various fuels for the purpose of heat and power generation. Their average contribution to the development of PM 1 was 15% and 51%, respectively, for the entire period of observations.