As part of a regional project of the study of pollution in two alpine valleys (POVA), an intensive campaign of measurements for VOCs, carbonyl compounds, PM 10 , particles and major ionic species was performed in Maurienne Valley (French Alps) during one week in August 2000. In summer, under anticyclonic conditions, the dispersion of air pollutants in deep valleys is mainly dependent on an usual characteristic cycle: up-valley wind for the day, down-valley wind for the night. During the sampling campaign, the diurnal variation west-east wind was changed by a South wind for two days. A saharan dust episode occurred, characterized by large increases of PM 10 , large particles, and Ca 2+. This dust episode was followed by an increase of fine particles (0.3 µm) and of SO 4 2-. , indicating the intrusion of an anthropogenic air mass. The evolution of VOCs have been influenced by these events and the concentration levels were higher during this period. The ratio benzene/ toluene was low (0.7) during the episode, which indicates an urban pollution.