Size-segregated aerosol chemical composition at a boreal site in southern Finland, during the QUEST project
[摘要] Size-segregated aerosol samples were collected during the QUEST fieldcampaign at Hyytiälä, a boreal forest site in Southern Finland,during spring 2003. Aerosol samples were selectively collected during bothparticle formation events and periods in which no particle formationoccurred.
A comprehensive characterisation of the aerosol chemical properties(water-soluble inorganic and organic fraction) and an analysis of therelevant meteorological parameters revealed how aerosol chemistry andmeteorology combine to determine a favorable "environment" for newparticle formation. The results indicated that all events, typically favoredduring northerly air mass advection, were background aerosols (total massconcentrations range between 1.97 and 4.31 µg m-3), with anincreasingly pronounced marine character as the northerly air flow arrivedprogressively from the west and, in contrast, with a moderateSO2-pollution influence as the air arrived from more easterlydirections. Conversely, the non-event aerosol, transported from the south, exhibitedthe chemical features of European continental sites, with a marked increasein the concentrations of all major anthropogenic aerosol constituents. Thehigher non-event mass concentration (total mass concentrations range between 6.88 and16.30 µg m-3) and, thus, a larger surface area, tended to suppressnew particle formation, more efficiently depleting potential gaseousprecursors for nucleation. The analysis of water-soluble organic compoundsshowed that clean nucleation episodes were dominated by aliphatic biogenicspecies, while non-events were characterised by a large abundance of anthropogenicoxygenated species. Interestingly, a significant content of α-pinenephoto-oxidation products was observed in the events aerosol, accounting for, onaverage, 72% of their WSOC; while only moderate amounts of these specieswere found in the non-event aerosol. If the organic vapors condensing ontoaccumulation mode particles are responsible also for the growth of newlyformed thermodynamically stable clusters, our finding allows one topostulate that, at the site, α-pinene photo-oxidation products (andprobably also photo-oxidation products from other terpenes) are the mostlikely species to contribute to the growth of nanometer-sized particles.
