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A preliminary multiple resistance routine for deriving dry deposition velocities from measured quantities

Author(s): Hicks BB, Baldocchi DD, Meyers TP, Hosker RP, Matt JR, et al.


Because there is no simple device capable of measuring the dry deposition rates of small particles and trace gases directly, much current activity is focused on the use of an inferential technique. In this method, measurements of atmospheric concentration (C) of selected chemical species are coupled with evaluations of appropriate deposition velocity (V d ) to yield estimates of dry deposition rate from their product. Difficulties arise concerning the ability to measure C, and especially regarding the poor knowledge of V d for many species. A multiple resistance routine for deriving deposition velocities is presented here. Current knowledge of biological processes is incorporated into a first-generation lsbig leaf’ model; formulations of resistances appropriate for describing individual leaves are combined to simulate the canopy as a whole. The canopy resistance is combined with estimates of aerodynamic and boundary-layer resistances to approximate the total resistance to transfer, from which deposition velocity is then computed. Special emphasis is given to the influence of the diurnal cycle, to the way in which the various transfer resistances can be inferred from routine data, and to the role of canopy factors (e.g., leaf area index, wetness, temperature response, and sunshade fractions).