This report describes the implementation and the application of Kalman Filter rountines around the model REM3/CALGRID employed at the Free University of Berlin (FUB) in the framework of the FUB-project 'Entwicklung eines Modellsystems für das Zusammenspiel von Messung und Rechnung für die bundeseinheitliche Umsetzung der EU-Rahmenrichtlinie Luftqualität'. Results are presented for a number of simulations for July 2001: 1. Assimilation of only O3 measurements. 2, Assimilation of only NO2 measurements. 3. Assimilation of both O3 and NO2 measurements.