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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 8, issue 10
Atmos. Meas. Tech., 8, 4453–4473, 2015
https://doi.org/10.5194/amt-8-4453-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Meas. Tech., 8, 4453–4473, 2015
https://doi.org/10.5194/amt-8-4453-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 Oct 2015

Research article | 22 Oct 2015

Ambient measurements of aromatic and oxidized VOCs by PTR-MS and GC-MS: intercomparison between four instruments in a boreal forest in Finland

M. K. Kajos1, P. Rantala1, M. Hill2, H. Hellén3, J. Aalto4, J. Patokoski1, R. Taipale1, C. C. Hoerger2, S. Reimann2, T. M. Ruuskanen1, J. Rinne1,3,5, and T. Petäjä1 M. K. Kajos et al.
  • 1Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland
  • 2Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Air Pollution/Environmental Technology, Überlandstr. 129, 8600 Dübendorf, Switzerland
  • 3Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
  • 4Department of Forest Ecology, Hyytiälä forestry field station, Hyytiäläntie 124, 35500 Korkeakoski, Finland
  • 5Department of Geosciences and Geography, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland

Abstract. Proton transfer reaction mass spectrometry (PTR-MS) and gas chromatography mass spectrometry GC-MS) are commonly used methods for automated in situ measurements of various volatile organic compounds (VOCs) in the atmosphere. In order to investigate the reliability of such measurements, we operated four automated analyzers using their normal field measurement protocol side by side at a boreal forest site. We measured methanol, acetaldehyde, acetone, benzene and toluene by two PTR-MS and two GC-MS instruments. The measurements were conducted in southern Finland between 13 April and 14 May 2012. This paper presents correlations and biases between the concentrations measured using the four instruments. A very good correlation was found for benzene and acetone measurements between all instruments (the mean R value was 0.88 for both compounds), while for acetaldehyde and toluene the correlation was weaker (with a mean R value of 0.50 and 0.62, respectively). For some compounds, notably for methanol, there were considerable systematic differences in the mixing ratios measured by the different instruments, despite the very good correlation between the instruments (mean R = 0.90). The systematic difference manifests as a difference in the linear regression slope between measurements conducted between instruments, rather than as an offset. This mismatch indicates that the systematic uncertainty in the sensitivity of a given instrument can lead to an uncertainty of 50–100 % in the methanol emissions measured by commonly used methods.

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