BACKGROUND AIR POLLUTION PREDICTION OVER SLOVENIA BY QUALEARIA MODELLING SYSTEM - PRELIMINARY VALIDATION Primož Mlakar 1 , Marija Zlata Božnar 1 , Boštjan Grašič 1 and Giuseppe Calori 2 1 MEIS d.o.o., Mali Vrh pri Šmarju 78, SI-1293 Šmarje - Sap, Slovenia 2 ARIANET Srl, Via Gilino n. 9, 20128 Milano, Italy Abstract: Slovenia is a country of very complex terrain and many problems with air pollution in the valleys, canyon and basins, where industrial air pollution is combined with traffic and domestic heating air pollution, giving rise to problems for the health impact and the ecosystems directly or indirectly. Among indirect effects is also effect on solar radiation budget because of photochemical smog and especially particles air pollution. To assess air pollutants over the country, a preliminary application of an experimental forecast system is presented here, with the aim of exploring its potentials and limitations in modelling the background air quality, and to focus the aspects where improvements are needed for a true operational use. Key words: air pollution, prediction, modelling system, validation, complex terrain INTRODUCTION Slovenia is a country predominantly characterized by complex terrain and with several problems of air pollution, mostly concerning PM10, NOx and ozone. The small scale air pollution control system “KOoreg” has been constructed for Zasavje region in the central part of the country (KOoreg, 2013), with details reported on the previous HARMO conference (Mlakar, P. et al., 2012). One of the important issues in construction of small scale air pollution modelling systems is the amount of the pollutants transport coming from other regions. Nevertheless, at present there are no operational modelling systems covering whole Slovenia and its neighbourhood in on-line mode, so to obtain an accurate estimation of the pollutants income into the Zasavje region we have connected KOoreg modelling system with QualeAria system (QualeAria, 2013) that is run continuously for Italy and neighbouring countries.. In order to correctly use air pollution transport data it has to be validated first. QUALEARIA SYSTEM QualeAria air pollution forecasting system (QualeAria, 2013) is operationally run by ARIANET (Milano), It is part of the MINNI Italian national modelling system (Zanini G. et al., 2005) and is based on the same meteorological and air quality models; specifically, its main components are:  a meteorological downscaling produced by mean of the NWP Model RAMS, starting from GFS synoptic scale weather forecasts distributed by the US weather Service (NCEP);  the Italian (ISPRA 2005, then updated to subsequent years) and European emission inventories (Denier van der Gon, HAC et al., 2009), developed by TNO within the EC FP7 Project MEGAPOLI, used to describe both point and area sources emissions;  the FARM Eulerian chemical-transport model (Silibello, C. et al., 2008; EEA MDS, 2013), applied to predict transport and chemical transformations for gaseous and particulate pollutants;  boundary conditions provided by the global scale chemical weather forecast produced by MATCH- MPIC model (Lawrence, M. G., 1999), run at the Max-Planck-Institut für Chemie in Mainz. The system is currently configured on two nested computational grids, the wider covering Europe at 48 km horizontal resolution and the smaller covering Italy and Slovenia at 12 km resolution. PREDICTION RESULTS OVER SLOVENIA Slovenia is placed in the inner part of the second modelling domain, far enough from domain border so that the results for Slovene territory are well estimated. QualeAria produces air pollution forecasts for state of Slovenia for 2 days in advance in 1h time resolution. Predictions of main pollutants from this configuration are included on a daily basis on KOoreg web site (Figure 1), to explore the potentials and limitations of the current system in modelling the background air quality in various part of the country, and to focus the aspects where improvements are needed.