A Numerical Method for Determining the Dry Deposition of Atmospheric Trace Constituents

Abstract

A diagnostic deposition model (DIADEM) based on the generally-accepted micrometeorological laws of the transfer of momentum, sensible heat and matter near the earth’s surface will be presented.

The model evaluates deposition fluxes and velocities of long-lived atmospheric trace gases by means of a detailed determination of the micrometeorological quantities such as the friction velocity u_*, the temperature and humidity scales ⊝_* and q_*, the roughness length z_o and the zero-displacement d. The parameterization of the fluxes is founded on the flux-gradient relationships in the turbulent region of the surface layer and the sublayer Stanton number as well as the Reynolds’ analogy between concentration, temperature and wind velocity distributions in the underlying sublayer. The model requires only the vertical profile data of wind velocity, dry and wet bulb temperatures and trace gas concentrations from the turbulent part of the surface layer.

DIADEM has been applied to vertical profile data collected in field experiments such as the GREIV I 1974 project and the Great Plains Turbulence Project.

In order to illustrate in which way the model can also be used to evaluate deposition fluxes and velocities of reactive trace gases, the method has been applied to observed concentrations of NO, NO₂ and O₃.