ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-5-465-2005 Eddy covariance flux measurements of biogenic VOCs during ECHO 2003 using proton transfer reaction mass spectrometry Spirig C. 1 Neftel A. 1 Ammann C. 1 Dommen J. 2 Grabmer W. 3 Thielmann A. 4 Schaub A. 5 Beauchamp J. 3 Wisthaler A. 3 Hansel A. 3 Agroscope, Swiss Federal Research Station for Agroecology and Agriculture, Reckenholzstr. 191, 8046 Zürich, Switzerland Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, Villigen, Switzerland Institute of Ion Physics, University of Innsbruck, Austria Max Planck Institute for Chemistry, Mainz, Germany Research Centre Jülich, Germany 15 02 2005 5 2 465 481 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/5/465/2005/acp-5-465-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/5/465/2005/acp-5-465-2005.pdf

Within the framework of the AFO 2000 project ECHO, two PTR-MS instruments were operated in combination with sonic anemometers to determine biogenic VOC fluxes from a mixed deciduous forest site in North-Western Germany. The measurement site was characterised by a forest of inhomogeneous composition, complex canopy structure, limited extension in certain wind directions and frequent calm wind conditions during night time. The eddy covariance (EC) technique was applied since it represents the most direct flux measurement approach on the canopy scale and is, therefore, least susceptible to these non-ideal conditions. A specific flux calculation method was used to account for the sequential multi-component PTR-MS measurements and allowing an individual delay time adjustment as well as a rigorous quality control based on cospectral analysis. The validated flux results are consistent with light and temperature dependent emissions of isoprene and monoterpenes from this forest, with average daytime emissions of 0.94 and 0.3&micro;g&nbsp;m<sup>-2</sup>s<sup>-1</sup>, respectively. Emissions of methanol reached on average 0.087&micro;g&nbsp;m<sup>-2</sup>s<sup>-1</sup> during daytime, but fluxes were too small to be detected during night time. Upward fluxes of the isoprene oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were also found, being two orders of magnitude lower than those of isoprene. Calculations with an analytical footprint model indicate that the observed isoprene fluxes correlate with the fraction of oaks within the footprints of the flux measurement.