摘要： The monitoring of pollution is fundamental to guarantee the health and the safety of the environment and humans. In fact, pollution is strictly correlated to climate changes, acid rains and in disease occurrences. The Differential Absorption LIDAR (DIAL) is a remote sensing technique able to identify the chemical substances in the atmosphere. This method is able to give information along long distances (also larger than 1 km) and it is possible to provide the system with equatorial mounts, in order to extract areal or volumetric concentration field. In this work, the authors focus on the interaction of water vapour with minor chemical gas measurements. In fact, the DIAL equation is achieved assuming some hypothesis that could not be acceptable in any conditions. In the present paper is evaluated how water vapour could change the differential extinction coefficients and when influences the final measurements. Both analytical investigation and experimental measurement are provided. These methodologies have been applied to six pollutants: ammonia (NH3), Benzene (C6H6), Nitrogen Dioxide (NO2), Nitrous Oxide (N2O), Ozone (O3) and Sulphur Dioxide (SO2).