Influence of high-model grid resolution on photochemical modelling in very complex terrains

The study of photochemical pollution in very complex terrains, such as the Northeastern Iberian Peninsula (NEIP), is primarily influenced by local topography. This kind of study demands a high spatial resolution. In order to illustrate the influence of the grid resolution on tropospheric ozone levels, several simulations were carried out with MM5-EMICAT2000-CMAQ model using horizontal resolutions ranging from 8, 4 and 2 km and with 6 or 16 vertical layers during an episode of photochemical pollution (13-16 August 2000). High resolutions lead to improve discrete and categorical statistical parameters when evaluating the model against meteorological and air quality data. Results show that coarser grids tend to present a homogeneous and smoothened behaviour of wind flows. Also, results do not manage to describe the particularities of the circulations of the region. Coarser simulations underestimate maximum ozone levels since the grid resolution highly influences the formation and loss processes of ozone.