The role of VOC oxidation products in continental new particle formation
Aerosol physical and chemical properties and trace gas concentrations\nwere measured\n\nduring the QUEST field campaign in March–April, 2003, in Hyyti ¨ al\n¨ a, Finland.\n\nOur aim was to understand the role of oxidation products of VOC’s\nsuch as mono- and\n\nsesquiterpenes in atmospheric nucleation events. Particle chemical\n5 compositions were\n\nmeasured using the Aerodyne Aerosol Mass Spectrometer, and chemical\ncompositions\n\nof aerosol samples collected with low-pressure impactors and a high\nvolume sampler\n\nwere analysed using a number of techniques. The results indicate that\nduring and after\n\nnew particle formation, all particles larger than 50nm in diameter\ncontained similar\n\norganic substances that are likely to be mono- and sesquiterpene oxidation\nproducts.\n\nThe oxidation products identified in the high volume samples were\nshown to be mostly\n\naldehydes. In order to study the composition of particles in the 10–50nm\nrange, we\n\nmade use of Tandem Differential Mobility Analyzer results. We found\nthat during nucleation\n\nevents, both 10 and 50nm particle growth factors due to uptake of\nethanol\n\nvapour correlate strongly with gas-phase monoterpene oxidation product\n(MTOP) concentrations,\n\nindicating that the organic constituents of particles smaller than\n50nm in\n\ndiameter are at least partly similar to those of larger particles.\nWe furthermore showed\n\nthat particle growth rates during the nucleation events are correlated\nwith the gasphase\n\nMTOP concentrations. This indicates that VOC oxidation products may\nhave a\n\nkey role in determining the spatial and temporal features of the nucleation\nevents. This\n\nconclusion was supported by our aircraft measurements of new 3–10nm\nparticle concentrations,\n\nwhich showed that the nucleation event on 28 March 2003, started at\nthe\n\nground layer, i.e. near the VOC source, and evolved together with\nthe mixed layer. Furthermore,\n\nno new particle formation was detected upwind away from the forest,\nabove\n\nthe frozen Gulf of Bothnia.