Pollution transport and transformation over the Po Plain as revealed by airborne and ground-based measurements in July 2017 during EMeRGe

Abstract. Airborne measurements provide valuable information about the vertical distribution of pollutants enabling the complex transport and dispersion pathways within and above the boundary layer (BL) to be investigated. In this study, the transport of pollution within the Po Plain, a major atmospheric pollution hotspot in Europe, was explored by exploiting airborne measurements made within the EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) project in combination with in situ and ground-based remote-sensing measurements over the whole Po basin. The analysis considers three areas where pollution emission and mixing are dominated by different processes: the Gulf of Venice to the east, the central part of the Po Plain, and the Gulf of Genoa to the west. Wind fields and backward trajectories during the days of the flights indicate the impact of the sea and mountain breezes on the BL distribution of pollutants, and of synoptic scale transport above it. Overall, the extensive data set of primary and secondary trace gases and aerosols at different altitudes provides insight into the effect of vertical and horizontal dynamical mixing on the chemical processing of pollutants within the BL. In this context, mixing of pollution plumes during stagnant conditions within the BL, stratification, venting and export of pollutants towards the Adriatic coast were observed. In addition, desert dust layers of Saharan origin at different altitudes confirm the mixing of naturally occurring dust and its impact on air quality of the lowermost atmosphere over the Po Plain.