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Atmospheric particulate matter (PM) was fractionated in six aerodynamicsizes, > 7.2, 7.2–3, 3–1.5, 1.5–1, 1–0.5 and < 0.5 μm, usinga cascade impactor. These fractions were collected at urban and rural sitesduring warm and cold seasons. Organic tracer compounds, such as levoglucosan,isoprene, pinene oxidation products, polycyclic aromatic hydrocarbons and quinones, wereanalyzed by gas chromatography coupled with mass spectrometry. These analysesshowed that the composition in the smallest size fractions(< 0.5 μm) was more uniform than in the larger sizes(7.2> PM > 0.5 μm). Thus, markers of photochemicallysynthesized organic compounds or combustion sources, either biomass burningor traffic emissions, were predominantly observed in the fraction< 0.5 μm, whereas the larger particles were composed of mixedsources from combustion processes, vegetation emissions, soil resuspension,road dust, urban lifestyle activities and photochemically synthesizedorganic compounds.  Important seasonal differences were observed at the rural site. In the< 0.5 μm fraction these were related to a strong predominance ofbiomass burning in the cold period and photochemically transformed biogenicorganic compounds in the warm period. In the7.2 > PM > 0.5 μm fractions the differences involvedpredominantly soil-sourced compounds in the warm period and mixed combustionsources, photochemical products and vegetation emissions in the cold.Multivariate curve resolution/alternating least squares showed that theseorganic aerosols essentially originated from six source components. Four ofthem reflected primary emissions related to either natural products, e.g.,vegetation emissions and upwhirled soil dust, or anthropogeniccontributions, e.g., combustion products and compounds related to urbanlifestyle activities like vehicular exhaust and tobacco smoking. Twosecondary organic aerosol components were identified. They accumulated in thesmallest (< 0.5 μm) or in the larger fractions(> 0.5 μm) and involved strong or mild photochemicaltransformations of vegetation precursor molecules, respectively.Toxicologically relevant information was also disclosed with the presentapproach. Thus, the strong predominance of biomass burning residues at therural site during the cold period involved atmospheric concentrations ofpolycyclic aromatic hydrocarbons that were 3 times higher than at theurban sites and benzo[a]pyrene concentrations above legal recommendations

Particle size-resolved source apportionment of primary and secondary organic tracer compounds at urban and rural locations in Spain