Size Distribution Characteristics of Organic Species in Atmospheric Particulate Matter from Finnish and German Rural Sites with Variable Anthropogenic Influence

Atmospheric aerosol particles were collected in a German urban/industrial influenced grassland location (Melpitz) and in a Finnish forest area (Hyytiälä) using a cascade impactor sampler. A labor-intensive analytical technique was applied to achieve a detailed chemical speciation of organic aerosols. Concentrations and size distributions were obtained for solvent-extractable organic compound series, as well for polyhydroxymono- and dicarboxylic acids, polyols, and sugars in the water extracts. The particulate matter contained mainly acids and aliphatic components and minor levels of alcohols, aldehydes, ketones, and aromatic compounds. The mass distribution of compounds presented a mode for submicrometric diameters, confirming the secondary origin of aerosol products formed by nucleation processes in the gas phase. Another mode was present for compounds in particles with coarser diameters, as a result of condensation on the surface of the pre-existing particles or else mechanical processes. The water-extractable acid compounds occurred mainly in the fine particles (Dp < 1.3 µm), in agreement with a possible secondary origin. Polyols and most sugars presented size distributions with variable fine or coarse maximum, depending on the location. Possible primary and secondary sources of polyhydroxylated compounds are discussed.