Abstract. We present a novel high-resolution inverse modelling system (“FLEXVAR”) based on FLEXPART-COSMO back trajectories driven by COSMO meteorological fields at 7 km×7 km resolution over the European COSMO-7 domain and four-dimensional variational (4DVAR) data assimilation technique. FLEXVAR is coupled offline with global TM5-4DVAR to provide background mole fractions (“baselines”) consiste...