Vertical advection and nocturnal deposition of ozone over a boreal pine forest Ü. Rannik1, I. Mammarella1, P. Keronen1, and T. Vesala1,2 1Department of Physical Sciences, P.O. Box 64, 00014 University of Helsinki, Helsinki, Finland 2Department of Forest Ecology, P.O. Box 27, 00014 University of Helsinki, Helsinki, Finland
Abstract. Night-time ozone deposition for a Scots pine forest in Southern Finland was
studied at the SMEAR II measurement station by evaluating the turbulent eddy
covariance (EC), storage change and vertical advection fluxes. Similarly to
night-time carbon dioxide flux, the eddy-covariance flux of ozone was
decreasing with turbulence intensity (friction velocity), and storage change
of the compound did not compensate the reduction (well-known night-time
measurement problem). Accounting for vertical advection resulted in
invariance of ozone deposition rate on turbulence intensity. This was also
demonstrated for carbon dioxide, verified by independent measurements of NEE
by chamber systems. The result highlights the importance of advection when
considering the exchange measurements of any scalar. Analysis of aerodynamic
and laminar boundary layer resistances by the model approach indicated that
the surface resistance and/or chemical sink strength was limiting ozone
deposition. The possible aerial ozone sink by known fast chemical reactions
with sesquiterpenes and NO explain only a minor fraction of ozone sink. Thus
the deposition is controlled either by stomatal uptake or surface reactions
or both of them, the mechanisms not affected by turbulence intensity.
Therefore invariance of deposition flux on turbulence intensity is expected
also from resistance and chemical sink analysis.
Citation: Rannik, Ü., Mammarella, I., Keronen, P., and Vesala, T.: Vertical advection and nocturnal deposition of ozone over a boreal pine forest, Atmos. Chem. Phys., 9, 2089-2095, doi:10.5194/acp-9-2089-2009, 2009.