[Graus2009] "Field performance and identification capability of the Innsbruck PTR-TOF",
EGU General Assembly Conference Abstracts
, vol. 11, pp. 10200, 2009.
Over the last one and a half decades Proton Transfer Reaction Mass Spectrometry (PTR-MS) [1, 2] has gained recognition as fast on-line sensor for monitoring volatile organic compounds (VOC) in the atmosphere. Sample collection is very straight forward and the fact that no pre-concentration is needed is of particular advantage for compounds that are notoriously difficult to pre-concentrate and/or analyze by gas chromatographic (GC) methods. Its ionization method is very versatile, i.e. all compounds that perform exothermic proton transfer with hydronium ions - and most VOCs do so - are readily ionized, producing quasi-molecular ions VOC.H+. In the quasi-molecular ion the elemental composition of the analyte compound is conserved and allows, in combination with some background knowledge of the sample, conclusions about the identity of that compound. De Gouw and Warneke (2007)  summarized the applicability of PTR-MS in atmospheric chemistry but they also pointed out shortcomings in the identification capabilities. Goldstein and Galbally (2007)  addressed the multitude of VOCs potentially present in the atmosphere and they emphasized the gasphase-to-aerosol partitioning of organic compounds (volatile and semi-volatile) in dependence of carbon-chain length and oxygen containing functional groups. In collaboration with Ionicon and assisted by TOFWERK we developed a PTR time-of-flight (PTR-TOF) instrument that allows for the identification of the atomic composition of oxygenated hydrocarbons by exact-mass determination. A detection limit in the low pptv range was achieved at a time resolution of one minute, one-second detection limit is in the sub-ppbv range. In 2008 the Innsbruck PTR-TOF was field deployed in the icebreaker- and helicopter based Arctic Summer Cloud Ocean Study (ASCOS) to characterize the organic trace gas composition of the High Arctic atmosphere. During the six-week field campaign the PTR-TOF was run without problems even under harsh conditions in the open water and during ice breaking. Continuous time-series of full mass spectra with a one minute time resolution were recorded throughout the campaign between August 2nd and September 7th 2008 running up to a net VOC data set of 745 hours. Over 370 mass peaks have been separated, about 340 show signal intensities above the 30 minute detection limit of 3pptv. Additionally we analyzed samples from nine helicopter based soundings providing vertical VOC profiles up to 3000 m.a.s.l. The performance of the newly developed instrument will be discussed and ASCOS data will be shown. Acknowledgment: The ASCOS expedition was arranged by the Swedish Polar Research Secretariat (SPRS) and was an effort within the framework of SWEDARCTIC 2008. For more information on ASCOS see http://ascos.se/. We thank the ASCOS organizers - Caroline Leck and Michael Tjernström - all ASCOS participants, the SPRS and the Oden crew for the excellent team work and Armin Wisthaler for his assistance in planning and preparations. The TOF-MS system was funded by the University of Innsbruck (Uni Infrastruktur Programm). The development project was financially supported by the Austrian Research Funding Association (FFG).  Hansel, A.; Jordan, A.; Holzinger, R.; Prazeller, P.; Vogel, W.; Lindinger, W. International Journal of Mass Spectrometry and Ion Processes 1995, 149-150, 609-619.  Lindinger, W.; Hansel, A.; Jordan, A. Chemical Society Review 1998, 27, 347-375.  De Gouw, J. A.; Warneke, C. Mass Spectrometry Reviews 2007, 26, 223-257.  Goldstein, A. H.; Galbally, I. E. Environmental Science and Technology 2007, 41, 154-1521.
[Eerdekens2009a] "Flux estimates of isoprene, methanol and acetone from airborne PTR-MS measurements over the tropical rainforest during the GABRIEL 2005 campaign",
Atmospheric Chemistry and Physics
, vol. 9, no. 13: Copernicus GmbH, pp. 4207–4227, 2009.
Tropical forests are a strong source of biogenic volatile organic compounds (BVOCs) to the atmosphere which can potentially impact the atmospheric oxidation capacity. Here we present airborne and ground-based BVOC measurements representative for the long dry season covering a large area of the northern Amazonian rainforest (6–3° N, 50–59° W). The measurements were conducted during the October 2005 GABRIEL (Guyanas Atmosphere-Biosphere exchange and Radicals Intensive Experiment with the Learjet) campaign. The vertical (35 m to 10 km) and diurnal (09:00–16:00) profiles of isoprene, its oxidation products methacrolein and methyl vinyl ketone and methanol and acetone, measured by PTR-MS (Proton Transfer Reaction Mass Spectrometry), have been used to empirically estimate their emission fluxes from the forest canopy on a regional scale. The mixed layer isoprene emission flux, inferred from the airborne measurements above 300 m, is 5.7 mg isoprene m−2 h−1 after compensating for chemistry and 6.9 mg isoprene m−2 h−1 taking detrainment into account. This surface flux is in general agreement with previous tropical forest studies. Inferred methanol and acetone emission fluxes are 0.5 mg methanol m−2 h−1 and 0.35 mg acetone m−2 h−1, respectively. The BVOC measurements were compared with fluxes and mixing ratios simulated with a single-column chemistry and climate model (SCM). The inferred isoprene flux is substantially smaller than that simulated with an implementation of a commonly applied BVOC emission algorithm in the SCM.