RESUMEN
Air pollutants concentration in the urban air strongly depends on the properties of the planetary boundary layer (the lower region of the atmosphere), roughly up to 1 km from Earth's surface. Radioactive radon gas has been recognised by various authors as a valuable natural tracer of transport and dispersion within this layer. To achieve a better comprehension of the urban pollution dynamic in the town of Alessandria, situated in the Po Valley in the north-west of Italy, a system for continuous measurement of radon concentration in outdoor air was experimented. This paper presents the first results obtained: the hourly trend of radon concentration in the diurnal course during different seasons and its correlation with the concentration of the major urban pollutants.