The Po-valley in Northern Italy has been identified as a hot spot area in Europe where pollutant levels are expected to remain problematic in the years to come. High anthropogenic emissions in combination with frequently occurring stagnant atmospheric conditions cause very high concentrations of pollutants. Sensitivity tests for one winter month have shown that the nudging of observational data into the mesoscale meteorological model MM5 does significantly improve the simulation of frequent low wind regimes, and as a consequence in certain conditions increases and improves modelled particulate matter (PM) concentrations. The focus of this work is to extend the study and assess the effect of MM5 nudging options during summer. We analyse here the impact of different observation nudging options on simulated PM10, and summer ozone using the CHLMERE model. Strengths and weaknesses of nudging approaches in one of the most polluted and complex topography areas in Europe are discussed.