A mesoscale meteorological model with passive tracers is applied in order to analyze transport from the atmospheric boundary layer to the free troposphere. The validation of the model against aircraft measurements indicates that the model adequately simulates the tracer distributions in the free troposphere as well as in the boundary layer. Budget calculations of passive tracers are performed in order to estimate the amount of transport in the area of a frontal system. The results show a very effective uplift associated in particular with a WCB transporting up to ~70% of a passive tracer initialized in the boundary layer to the free troposphere within 3 days. ¿ 2001 American Geophysical Union