AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Ultra-High Resolution Mass Spectrometry Analysis of PM1 Finnish Boreal Forest Aerosol
IVAN KOURTCHEV, Stephen Fuller, Juho Aalto, Taina Ruuskanen, Willy Maenhaut, Markku Kulmala, Markus Kalberer, University of Cambridge
Abstract Number: 199 Working Group: Aerosol Chemistry
Abstract A substantial fraction of atmospheric fine particulate matter is comprised of organic compounds which cover a wide range of polarities, volatilities and masses. Our knowledge on the organic chemical composition of atmospheric aerosols is rather limited; only about 20-30% of the organic matter has been characterised at the molecular level. Because of this limitation, recent efforts have focused on methods that classify bulk organic aerosols. Ultra-high resolution mass spectrometry (UHR-MS) allows determination of thousands of individual organic aerosol constituents at once, providing their elemental formulae from accurate mass measurements.
In this study, we applied UHR-MS for the analysis of PM1 samples collected during a two-week summer period (August, 2011) at a boreal forest site (Hyytiälä), southern Finland. Almost for all samples negative ionisation spectra contained significantly more ions than those of positive, and the majority of these ions were found below 350 Da. More than 1000 elemental formulae were assigned in both modes, and no apparent diel variations in the elemental compositions were observed. The majority of the peaks were attributed to oxygenated or nitrogen containing compounds. The peak assignments were examined using a van Krevelen approach, which allows describing the distribution of functional groups in organic aerosol (OA). On average, the O:C ratios were found to be around 0.5 and 0.2 in the negative and positive modes, respectively. The molecular composition of the examined samples was influenced by the air mass back trajectories. In general, the O:C ratio was within the range obtained for secondary OA generated in laboratory experiments with a number of biogenic volatile organic compounds (BVOCs) reported in recent studies for alpha-pinene and isoprene. The additional LC/MS analysis revealed more than 30 species, which were mainly attributed to oxidation products of BVOCs (i.e., alpha-, beta-pinene and delta-3-carene) supporting the results from the analysis of the bulk OA.