| Summary: | The size distribution and chemical composition of ambient aerosols were analyzed using an Aerodyne aerosol mass spectrometer (AMS) at Preila station during 3-15 September 2006. The major observed components of the aerosol were sulfates and organics with a smaller amount of nitrates and ammonium. Large contribution of organics was established in all air masses, but it reached 60% of all aerosol mass in North Atlantic marine air masses. The origin of chemical aerosol components was interpreted when size distribution spectra were analyzed. Mainly two modes were registered both for sulfates and organics - one in the accumulatation range, the other in the supermicron range. The diameter of sulfates in accumulation mode different from that of organics in clean marine air mass: they were about 270 nm and 170 nm respectively. This difference showed different sources or transformation mechanisms of sulfates and organics. In the case of polluted air masses the anthropogenic origin of both components was dominant, thus diameters became equal and were about 400 nm, showing dominant secondary production mechanism.
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