The German Environment Agency (UBA) funded the project “Influence of a major airport on temporal and spatial distributions of outdoor air concentrations of ultrafine dust <100 nm to describe the potential exposure in the vicinity - including other air pollutants (soot, nitrogen oxides and particulate matter (PM2.5 and PM10))”, UFOPLAN 3716 52 200 0. Total UFP number concentration for the year 2015 at and around Frankfurt Airport (FRA) was estimated using a combination of established small-scale (LASAT/LASPORT) and large-scale modelling (EURAD, MADE). Emissions were determined for aircraft traffic, road traffic, airport ground services and regional/mesoscale background using standard national and international inventories (HBEFA, ICAO, GRETA) and specific data obtained from the airport. Model outputs were series of successive 3-dimensional hourly mean concentrations apportioned to aircraft, airport, motor traffic and background. The model results suggest that aircraft main engines are the dominant source of UFP at the airport. Aircraft up to 3’000 ft (about 230’000 LTOs) plus airport-bound sources yield an annual nvPM emission of 1e+24 particles, about 90% of which are due to aircraft main engines. ... mehrAccording to the model results, long-time averages of UFP number concentration are dominated by background contributions at locations further away from the airport, while the airport contribution to hourly mean concentrations can be significant even in some distance from the airport. An important aim of the project was to identify shortcomings of current state-of-the-art emission and concentration modelling of UFP in the context of airports. Here, inconsistent UFP diameter ranges in the databases, models and measurements are of relevance, likewise differences in the considered UFP characterisation and measuring method, in particular volatile versus non-volatile fractions. On a more advanced level, current limitations in knowledge and capabilities of local models to address UFP transformation processes play a role.