The ISOTROP project was a response to the ESA ITT "Impact of Spaceborne Observations on Tropospheric Composition Analysis and Forecast", AO/1- 6845/11/NL/AF. The general aim is to assess the benefit of the LEO+GEO satellite system for the understanding of local to regional scale tropospheric composition with a focus on Europe. The ISOTROP consortium involved researchers from the European institutes CNRS-GAME, TNO, NILU, FMI, and was led by KNMI. The study focussed on Sentinel 5-P (S5P) and Sentinel 4 (S4) observations, with a sensitivity study for the Sentinel 5, which will have a different overpass time than Sentinel 5-P. The study focussed on four chemical species: NO2, HCHO, CO and O3.