Within the EU project PEGASOS extensive field campaigns took place in 2012 in the Netherlands and the Po Valley as well as 2013 in Southern Finland. The field campaigns integrated ground based measurements at the supersites in Cabauw, San Pietro Capofiume, and Hyytiälä with airborne measurements on board a Zeppelin NT air ship. The campaigns aimed at photochemistry, particle formation, and particle properties as a function of the diurnal evolution of the PBL with a focus on the link between the HOX cycle and particle formation and particles properties on one hand and role of dynamics in chemical and microphysical processes on the other hand. This session serves primarily to present results from the PEGASOS campaigns to a broader public. However, other contributions with a focus on the diurnal evolution of the PBL and its role in photochemistry and particle formation are welcome.