This work contributes to improvement in consequences evaluation for a release of radioactivity to the atmosphere at local scale. An investigation of how such an improvement could be achieved with the help of variational data assimilation is presented. The measurements collected in a wind tunnel experiment are coupled to a Gaussian puff model. Capacity of finding the true source emission rate is tackled in the first place. Secondly, data assimilation is employed to accommodate the computed concentration profiles to the measured ones. Benefit from data assimilation is subject to the quantity of information contained in the measurements. Therefore, posterior analysis of the monitoring network is carried out and its quality assessed.