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 revealed high bias of surface SO2 and O3 concentrations by the model, especially during nighttime hours. Comparison of the RADM results with surface measurements of hourly ozone concentrations from the National Dry Deposition Network (NDDN) sites showed distinct diurnal variations in the model high bias. Here, we investigate what part of this phenomenon is influenced by the coarse vertical resolution of RADM in representing the deposition layer. For certain deposition species in the model, we apply the planetary boundary layer (PBL) similarity theory to predict the high bias of the model results (volume averages) to the surface observations (time series at a point) for the horizontally homogeneous case. Here, we applied the profile corrections to a secondary species O3, which is one of active reacting species even at night especially with NO. However, we attempted to separate the effect of deposition layer thickness from the effects of other horizontal and vertical resolution such as emissions source distribution during the NO---O3 titration process for a clearer presentation of our hypothesis. The study shows that there are situations when a considerable portion of the high bias of model O3 concentrations at night is explained by the coarse vertical resolution in the deposition layer. It is shown that the model needs to resolve, at least, the lower half of the PBL in order to predict surface deposition fluxes correctly. Comparison with several NDDN observations shows that for certain NDDN sites the present hypothesis cannot fully explain the modelʹs high bias of daily minimum O3. In a companion paper, the effect of emission source distribution in representing the NO---O3 titration process will be studied to investigate causes of the model bias further.