DESIGN ARTIFACTS IN EULERIAN AIR-QUALITY MODELS - EVALUATION OF THE EFFECTS OF LAYER THICKNESS AND VERTICAL PROFILE CORRECTION ON SURFACE OZONE CONCENTRATIONS

Previous studies on the regional acid deposition model (RADM) have rev ealed high bias of surface SO2 and O-3 concentrations by the model, es pecially during nighttime hours. Comparison of the RADM results with s urface measurements of hourly ozone concentrations from the National D ry Deposition Network (NDDN) sites showed distinct diurnal variations in the model high bias. Here, we investigate what part of this phenome non is influenced by the coarse vertical resolution of RADM in represe nting the deposition layer. For certain deposition species in the mode l, we apply the planetary boundary layer (PBL) similarity theory to pr edict the high bias of the model results (volume averages) to the surf ace observations (time series at a point) for the horizontally homogen eous case. Here, we applied the profile corrections to a secondary spe cies O-3, which is one of active reacting species even at night especi ally with NO. However, we attempted to separate the effect of depositi on layer thickness from the effects of other horizontal and vertical r esolution such as emissions source distribution during the NO-O-3 titr ation process for a clearer presentation of our hypothesis. The study shows that there are situations when a considerable portion of the hig h bias of model O-3 concentrations at night is explained by the coarse vertical resolution in the deposition layer. It is shown that the mod el needs to resolve, at least, the lower half of the PBL in order to p redict surface deposition fluxes correctly. Comparison with several ND DN observations shows that for certain NDDN sites the present hypothes is cannot fully explain the model's high bias of daily minimum O-3. In a companion paper, the effect of emission source distribution in repr esenting the NO-O-3 titration process will be studied to investigate c auses of the model bias further.