ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-2-279-2002 Virtual disjunct eddy covariance measurements of organic compound fluxes from a subalpine forest using proton transfer reaction mass spectrometry Karl T. G. 1 5 Spirig C. 1 2 Rinne J. 1 3 Stroud C. 1 Prevost P. 1 Greenberg J. 1 Fall R. 4 Guenther A. 1 National Center for Atmospheric Research, Boulder, Colorado, USA Eidg. Forschungsanstalt für Agrarökologie und Landwirtschaft, Zürich, Switzerland now at: Centre National de Recherches Meteorologiques, Toulouse, France University of Colorado, Boulder, Colorado, USA present address: ACD, NCAR, PO 3000, Boulder, CO, 80307, USA 29 10 2002 2 4 279 291 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/2/279/2002/acp-2-279-2002.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/2/279/2002/acp-2-279-2002.pdf

A `virtual' disjunct eddy covariance (vDEC) device was tested with field measurements of biogenic VOC fluxes at a subalpine forest site in the Rocky Mountains of the USA. A PTR-MS instrument was used as the VOC sensor. Daily peak emission fluxes of 2-methyl-3-buten-2-ol (MBO), methanol, acetone and acetaldehyde were around 1.5, 1, 0.8 and 0.4 mg m<sup>-2</sup> h<sup>-1</sup>, respectively. High pass filtering due to long sampling lines was investigated in laboratory experiments, and suggested that VOC losses in PTFA lines are generally governed by diffusion laws. Memory effects and surface reactions did not seem to play a dominant role. Model estimates of MBO fluxes compared well with measured fluxes. The results also suggest that latent heat and sensible heat fluxes are reasonably well correlated with VOC fluxes and could be used to predict variations in VOC emissions. The release of MBO, methanol, acetone and acetaldehyde resulted in significant change of tropospheric oxidant levels and a 10--40% increase in ozone levels, as inferred from a photochemical box model. We conclude that vDEC with a PTR-MS instrument is a versatile tool for simultaneous field analysis of multiple VOC fluxes.