Characterisation of organic compounds in aerosol particles from a Finnish forest by on-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry.

During the European Union project Quantification of Aerosol Nucleation in the European Boundary Layer (QUEST), which began in spring 2003, atmospheric aerosol particles were collected in a Finnish Scots pine forest using a high-volume sampler. The organic compounds in the filter samples were then analysed by on-line coupled supercritical fluid extraction-liquid chromatography-gas chromatography-mass spectrometry (SFE-LC-GC-MS). The sample was first extracted by SFE. During LC the extracts were fractionated into three fractions according to polarity. The final separation was carried out by GC-MS. A fraction volume as high as 840 microL was transferred to the GC, using the partial concurrent eluent evaporation technique. The same instrumentation, with an in-situ SFE derivatisation method, was used to analyse organic acids. Major compounds such as n-alkanes and PAH were analysed quantitatively. Their concentrations were lower than those usually observed in urban areas or in other forest areas in Europe. The wind direction was one of the most important factors affecting changes in the daily concentrations of these compounds. Scots pine needles were analysed with the same system to obtain reference data for identification of biogenic compounds in aerosol particles. Other organic compounds found in this study included hopanes, steranes, n-alkanals, n-alkan-2-ones, oxy-PAH, and alkyl-PAH; some biogenic products, including oxidation products of monoterpenes, were also identified.