1. PREAMBLE In the last years, many studies have shown that the direct forcing of dust aerosol may be comparable to or even exceed the forcing of anthropogenic aerosols on both global and regional scales. The dust aerosols, besides of changing climate through the scattering and absorption of solar and thermal radiation, also affect the environment by fertilizing marine and terrestrial ecosystems, which in turn influence the carbon cycle. Moreover, the dust particles contribute substantially to the total aerosol mass usually employed in the developing of the environmental policy regulations, therefore, a reliable forecast of dust events is mandatory. Italy is often reached by dust produced in the Saharan regions. Analyzing the period 2000-2003, Mona et al. (2006) have shown that the dust intrusions in the south of Italy are frequent: about a day every 10 days and, in the north of Italy, Rogora et al. (2004) have seen a significant neutralization of precipitation associated to the increase of the dust event frequency in the period 1975-2001. To the scope of predicting the advection of dust and its physical and chemical properties over Italy, a dust emission scheme has been implemented in the air quality model BOLCHEM, which solves simultaneously the chemical and meteorological equations. The dust models rely heavily on the meteorological information, thus, the online coupling of meteorology to production, dynamics and chemistry of dust aerosols is beneficial. This coupling also allows a better representation of atmospheric processes, which often have a much smaller time scale than the meteorological output frequency (e.g. cloud and rainfall formation, wind speed and direction), involved in dust forecasts. The forecast of dust is particularly difficult since the dust emissions cannot be measured and are generally based on model calculations. Here, the dust- BOLCHEM modeling system is presented together with preliminary results that show the ability of the model to predict the Saharan dust intrusion over Italy. ACKNOWLEDGEMENTS This work was conducted in the frame of ACCENT and GEMS EC projects, Italian MIUR project AEROCLOUDS, and was also supported by the Italian Ministry of Environment through the Program Italy-USA Cooperation on Science and Technology of Climate Change. REFERENCES Buzzi, A., Fantini, M., Malguzzi, P., Nerozzi, F., 1994, Meteorol. Atmos. Phys., 53, 137-153. Buzzi, A., d'Isidoro, M., Diavolio, S., 2003, Q. J. R. Meteorol. Soc., 129, 1795-1818. Carter, W. P.L., 1990, Atmos. Environ., 24A, 481-518. Gery, W., Witten, G. Z., Killus, J. P., Dodge. M. C., 1989, J. Geophys. Res.,, 94, D10, 12925-12956. Marticorena, B., Bergametti, G., 1995, J. Geophys. Res., 16415-16430. Mircea, M., d'Isidoro, M., Maurizi, A., Vitali, L., Monforti, F., Zanini, G., Tampieri, F., 2007, submitted to Atmos.Environ. Mona, L, Amodeo, A. Pandolfi, M., Pappalardo, G., 2006, J. Geophys. Res., doi:10.1029/2005JD006569. Rogora, M., Mosello, R. and A. Marchetto, 2004, Tellus, 56B, 426-434. Tafuro,A.M., Barnaba, F., De Tomasi, F., Perrone, M.R., Gobbi, G.P., 2006, Atmos. Res., 67-93. Tegen, I., Harrison, S.P., Kohfeld, K, Colin Prentice, I, Coe, M., Heinmann,M., 2002, J.Geophys.Res., 107, D21, doi: 10.1029/2001JD000963. Tegen, I., Heinold, B., Todd, M., Helmert, J., Washington, R., Dubovik, O., 2006, Atmos.Chem.Phys., 6, 4345-4359. Regional modeling of aerosols using the air quality model BOLCHEM: Saharan dust intrusions over Italy Mihaela Mircea, Massimo D'Isidoro, Alberto Maurizi, Francesco Tampieri, Maria Cristina Facchini, Stefano Decesari, Sandro Fuzzi Istituto di Scienze dell’Atmosfera e del Clima, Consiglio Nazionale delle Ricerche, Bologna, Italy Dust model BOLCHEM The dust model implemented in BOLCHEM was developed by Tegen et al. (2002) and it is based on the results from Marticorena and Bergametti (1995). The horizontal and vertical dust fluxes are calculated based on the location of the preferential dust sources, soil texture, surface roughness, vegetation cover, soil moisture content and surface wind velocity. The ratio between the vertical and the horizontal dust fluxes varies with the type of soil and the size of the particle mobilized. The size distribution of the mobilized dust depends on both the surface properties (soil texture) and the surface wind speed. The threshold friction velocities used to initiate the dust emissions are computed as a function of particle size following Marticorena and Bergametti (1995), but assuming constant roughness within the model grid cells (0.001 cm). Moreover, the simulation shown here was carried out with a threshold friction velocity lowered by a factor of 0.75 since lower thresholds velocities improve model results compared to observations (Tegen et al., 2006). Further, the ratio between the vertical and the horizontal dust fluxes will be estimated from the comparison of calculated dust optical thickness with the observed one over Italy, to the scope of calibrating the dust concentrations calculated by the model. Heterogeneous chemistry Gas Chemistry (SAPRC90/CBIV) Winds, T, P, q, Clouds, Radiative Fluxes Dust model Transport & diffusion optical properties, cloud condensation nuclei BOLCHEM-DUST Flow Chart Meteorological Model (BOLAM) A comprehensive quantitative statistical evaluation of BOLCHEM results for few summer periods, at different sites in Italy, have shown that the model performs well with both gas chemistry models (Mircea et al., 2007). The differences in the predicted ozone Saharan Dust over Italy: July 16, 2003 AQUA/MODIS, 12:35 UTCBOLCHEM-DUST Red characters indicate the processes/interactions not implemented yet. concentrations obtained by employing the two chemical mechanisms are in agreement with those previously reported in literature and are due to different representations of VOC emissions and chemistry. BOLCHEM (Mircea et al., 2007) is a modeling system that comprise the meteorological model BOLAM (Buzzi et al., 1994, Buzzi et al., 2003), an algorithm for airborne transport and diffusion of pollutants and two photochemical mechanisms: SAPRC90 (Carter, 1990) and CB-IV (Gery et al., 1989). The meteorology is coupled online with the chemistry. Simultaneous integration of chemistry and meteorology (without any interpolation in time or space as generally performed by the offline air quality models) is a mandatory request for air quality forecasts over regions with complex topography, such as Italy. The comparison of the dust event occurred on 13 July 2003, simulated by BOLCHEM and seen by the AQUA/MODIS satellite/sensor, shows that the model is able to predict well both the extent and the timing of the dust event over Italy. In both images, it can be note that the plume of dust over the Mediterranean comes from north-west and north of Africa and goes straightforward to the center and north of Italy with only a little veil over Sicily and Messina Strait. These results substantiate that the model use reliable surface land/soil information, meteorological conditions and transport scheme.