Abstract
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.
Highlights
Ozone deposition into forest canopies and sink mechanisms at night are not well understood
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
The vertical advection term of ozone exchange accounted for a significant fraction of ozone transport under low turbulence conditions at night
Summary
Ozone deposition into forest canopies and sink mechanisms at night are not well understood. Ozone deposition has been studied by different methods, by canopy level micrometeorological as well as by shoot level measurements. The ozone deposition studies by micrometeorological methods at night-time conditions are further complicated by prevailing low-turbulence, stable conditions. A few studies have made effort in evaluation of the horizontal advection term, but because of spatial variability the uncertainty of this term is found to be in the same order as total ecosystem exchange (Aubinet et al, 2005). These studies, are focused only on carbon dioxide and not on any other compound
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