In densely settled areas, odours become more and more important in overall judgements of planning situations, where often emitting sites or residential sites are planned close together. In practice, especially public authorities have to take possible odour annoyances into consideration when odour-emitting sites were planned or increased. On the base of precompiled flow fields, a tool was developed, which can compute the dispersion of odours during nocturnal drainage flows. By using this tool, authorities are able to evaluate the necessary information about odour impacts in a fast, easy and cost-effective way. Since this screening tool covers the expanse of a whole state, it can be applied on a large number of projects.