Interpretation of the derivation of the ozone deposition velocity, expressed in terms of the traditional three-resistances, is analyzed to explain observed characteristics of the ozone deposition velocity. As formulated in some studies, the resistance ra is not closely related to the turbulent transfer of momentum, but instead related to the turbulent transfer of heat in the surface layer. The resistance rb also includes the influence of the turbulent transfer of heat in the surface layer, and does not directly represent the net effect of the direct turbulent transfer across the canopy layer and molecular
diffusion across the molecular sublayer. The resistance rc is much larger than the sum of the resistances of ra and rb, and is the leading resistance for determining the ozone deposition velocity. The resistance rc is not only associated with the ozone removal mechanisms at ground surfaces, such as stomatal uptake, soil and leaf surface removal, and chemical reactions, but also strongly influenced by the turbulent intensity in the surface layer.
The role of turbulence in ozone deposition is examined using tower data collected during the California Ozone Deposition Experiment (CODE). In addition to the ozone uptake by vegetation and soil surfaces, we find that the resistance rc is related to the friction velocity at night and the buoyancy flux during the day. The phase difference between the diurnal variation of turbulence, expect
ed photochemical production of ozone, and canopy transpiration reduces the potential capability of ozone uptake by canopy stomata. Significant ozone deposition occurs at night, and in the early morning when the stomata are not fully open. This indicates the importance of ozone transport by turbulence and ozone uptake processes at soil and non-transpiring canopy surfaces. The correlation between the ozone deposition velocity and the canopy photosynthesis is dominated by their diurnal cycles due to their association with the solar radiation. Only part of the ozone deposition is caused by the canopy stomatal uptake.
Symposium on Interdisciplinary Issues in Atmospheric Chemistry