Size and composition real-time measurements of atmospheric submicron aerosol (PM1) were conducted in the Lithuanian background and urban areas during several months (April-July, 2008) using the Quadrupole aerosol mass spectrometer (Q-AMS). The average mass concentration of non-refractory PM1 ranged within 8-13 mu g m(-3). Organic compounds of PM1 were the most abundant constituent ranging from 70 to 83%, nitrate made up 4.0-7.7%, ammonium 1.7-3.9%, sulfate 11-21%, and chloride less than 1%. While sulfate concentrations were comparable at the urban and background sites, concentrations of organic compounds and nitrate in Vilnius city were almost twice as high as those at the background site (Rugsteliskis). The average aerodynamic diameter for nitrate and organics was about 300 nm at both sampling sites in Vilnius city and at Rugsteliskis background site. The average aerodynamic diameter for ammonium was about 355 nm and for sulfate about 400 nm. The main source of organics and nitrates in the city was emission from traffic, however the main source of sulfates at urban and background sites was long-range transport. Positive matrix factorization (PMF) analysis of the unit mass-resolution (UMR) spectra was used to identify sources of organic matter in the urban (Vilnius) and background (Rugsteliskis) aerosol. Organic aerosol components were identified from AMS spectra for both sites: primary anthropogenic emissions-hydrocarbon-like organic aerosol (HOA), aged oxygenated low volatility organic aerosol (LV-OOA), and less oxygenated, presumably, semivolatile organic aerosol (SV-OOA) at the urban site (Vilnius city) as well as biomass burning organic aerosol (BBOA), aged oxygenated low volatility organic aerosol (LV-OOA), and semivolatile biogenic secondary organic aerosol (SV-OOA) at the background site (Rugsteliskis).