Journal Article

PreJuSER-10530

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Turbulent exchange and segregation of HOx radicals and volatile organic compounds above a deciduous forest

Dlugi, R. ; Berger, M. ; Zelger, M. ; Hofzumahaus, A.FZJ* ; Siese, M.FZJ* ; Holland, F.FZJ* ; Wisthaler, A. ; Grabmer, W. ; Hansel, A. ; Koppmann, R.FZJ* ; Kramm, G. ; Möllmann-Coers, M.FZJ* ; Knaps, A.FZJ*

2010
EGU Katlenburg-Lindau

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Please use a persistent id in citations: http://hdl.handle.net/2128/10052  doi:10.5194/acp-10-6215-2010

Abstract: The eddy covariance method was applied for the first time to estimate fluxes of OH and HO2 together with fluxes of isoprene, the sum of methyl vinyl ketone (MVK) and methacrolein (MACR) and the sum of monoterpenes above a mixed deciduous forest. Highly sensitive measurements of OH and HO2 were performed by laser induced fluorescence (LIF), and biogenic volatile organic compounds (BVOCs) were measured by Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) at a time resolution of 5 s, each. Wind speed was measured by a sonic anemometer at 10 Hz. The one-day feasibility study was conducted at a total height of 37 m, about 7 m above forest canopy, during the ECHO (Emission and CHemical transformation of biogenic volatile Organic compounds) intensive field study in July 2003. The daytime measurements yielded statistically significant OH fluxes directed downward into the direction of the canopy and HO2 fluxes mainly upward out of the canopy. This hints towards a significant local chemical sink of OH by reactions with BVOCs, other organic and inorganic compounds and conversion of OH to HO2 above the canopy. For OH the measured flux is locally balanced by chemical sources and sinks and direct transport of OH plays no important role for the local chemical OH budget at the measurement height, as expected from the short OH lifetime (<1 s). For HO2 the chemical lifetime (20 s) is in the range of the turbulent transport time for transfer between the top of the canopy and the measuring point. In this case, the radical balance is significantly influenced by both chemistry and transport processes. In addition, the highly time-resolved trace gas measurements were used to calculate the intensity of segregation of OH and BVOCs, demonstrating that the effective reaction rate of isoprene and OH was slowed down as much as 15% due to inhomogeneous mixing of the reactants. The paper describes the results, the applied methods and provides a detailed analysis of possible systematic errors of the covariance products.

Keyword(s): J

Note: This research was financially supported by the German Atmospheric Research Program 2000, project ECHO under grant No. 07ATF47. In addition, three of us (Ralph Dlugi, Martina Berger, Michael Zelger) were supported by special funding of Forschungszentrum Julich, Germany.The very valuable and detailed comments from two well knowledgeable and informed reviewers were most helpful. We also greatly appreciate comments by F. Rohrer to different versions of the manuscript. We thank M. Schatzmann, B. Leitl and the staff of the Meteorological Institute, University of Hamburg, Germany and H. J. Kirtzel, METEK GmbH, Germany for their generous support to calibrate the sonic anemometers in the Environmental Wind Tunnel Laboratory, Hamburg.

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Research Program(s):

1. Atmosphäre und Klima (P22)

Appears in the scientific report 2010

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