To assess the impact on citizens living in the surroundings of landfills, atmospheric dispersion models commonly represent the tool suggested by the guidelines in the field of odour. Among all the available dispersion models, the Lagrangian particle models and the puff models currently represent by far the most common tools to simulate odour dispersion from landfill. However, to make the results meaningful, several factors of uncertainty need to be taken into account. One of these is represented by the input data set supplied to the model. This paper discusses the sensitivity of the Lagrangian model SPRAY to the parameter ?z, which characterizes the emission vertical dimension, when assessing odour impact from landfills. A similar parameter is required by the CALPUFF model, which needs the definition of sz0 to set out the initial vertical dimension of the Gaussian puff. The choice of these variables is particularly critical, especially because no clear indications about their setting are available. This study shows a different behavior of the two models. For CALPUFF, the choice of sz0 may result in modelled odour concentrations at receptors that differ by up to a factor 5-6 in the vicinity of the emission source. On the other hand, the definition of ?z does not significantly affect SPRAY results.