The influence of surface-atmosphere exchange processes on ozone levels

A comprehensive modelling system taking into account emission, transport, dispersion, deposition and chemical transformation processes of gaseous pollutants has been used to simulate an ozone episode over the Piemonte Region in Northern Italy. A meteorological pre-processor (SURFPRO: SURface-atmosphere interFace PROcessor) has been developed and applied in order to estimate the parameters used to define the status of the lower part of the atmosphere commonly called the Planetary Boundary Layer (PBL). The vertical exchanges between surface and lower atmospheric layers are defined estimating momentum, heat and moisture turbulent fluxes and PBL depth. The capability of the atmosphere to vertically redistribute the pollutants is represented by vertical diffusivities. The influence of different land use areas on diffusivities and other turbulent scaling parameters is shown confirming the importance of adequate descriptions of the surface cover. The effects of terrain slopes and shadow projection on incoming solar radiation and consequently on beat exchanges are also shown. Finally the good agreement between observed and predicted ozone concentration by the Eulerian photochemical model FARM (Flexible Air quality Regional Model) confirms the capability of the modelling system and the meteorological pre-processor to correctly describe chemical and physical processes that lead to the formation and the accumulation of ozone in Northern Italy.