ON THE DRY DEPOSITION OF OZONE AND REACTIVE NITROGEN SPECIES

Dry deposition of ozone and reactive nitrogen species, such as NO, NO2 , NO3, N2O5, HNO3, NH3 and NH4NO3, is examined in the context of numer ical methods. These methods are based on the generally accepted microm eteorological ideas of the transfer of momentum, sensible heat, and ma tter near the Earth's surface, where chemical reactions among these tr ace species are considered. The fluxes in the turbulent region of the atmospheric surface layer are parameterized by first-order closure pri nciples. The uptake processes by vegetation and the soil are described by a Deardorff-type soil-vegetation-atmosphere transfer scheme. As in the case of HNO3 and NH3 the resistance of the system vegetation-soil against uptake of matter seems to be of minor importance, parameteriz ation approaches for the more important transfer resistances of the in terfacial sublayer adjacent to the surface are evaluated. The model re sults show that especially the dry deposition fluxes of reactive nitro gen species are not only influenced by micrometeorological and plant-p hysiological parameters, but also strongly affected by chemical reacti ons. In most cases, the fluxes of these trace constituents vary strong ly with height and often show a change of direction. These flux result s differ considerably from those derived with the constant flux approx imation, sometimes up to several hundred percent. Thus, in such cases the most widely used ''big leaf'' multiple resistance approach which i s based on the constant flux approximation seems to be inappropriate f or deriving dry deposition fluxes and deposition velocities of reactiv e nitrogen species.