3-day air quality forecast is carried out by the National and Kapodistrian University of Athens (NKUA) in collaboration with the Aristotle University of Thessaloniki (AUTH) using a modelling system which consists of the prognostic meteorological model WRF and the photochemical air quality model CAMx. The forecast system runs pre-operationally on a daily basis in order to predict air pollutants levels (O3, NO2, NO, CO, SO2, PM10) and radon concentrations (Rn). The forecast is performed in two spatial scales: 1) Regional scale (Europe, Balkan) and 2) Urban scale (Athens).