Observations of tropospheric peroxy radicals are a key point for interpretation of theprocessing and transformation of polluted outflows from major populated centers (MPCs). Aseries of European and Asian MPCs are investigated by the project EMeRGe (Effect ofMegacities on the transport and transformation of pollutants on the Regional and Globalscales). With this objective two airborne campaigns using the research platform HALO (HighAltitude and LOng Range aircraft) were carried out over Europe in summer 2017 and in EastAsia in spring 2018. The Institute of Environmental Physics (IUP) in Bremen participated in both EMeRGecampaigns with the airborne measurement of the total sum of peroxy radicals, RO2∗=(HO2 + ∑ RO2), by using the home made PeRCEAS instrument based on the combinationof the PERCA (peroxy radical chemical amplification) and CRDS (cavity ring downspectroscopy) techniques. One of the main purposes of the campaigns was the investigationof MPC outflow at the local and regional scales. Within the EMeRGe targeting MPCs inEurope and Asia, Rome and Manila are selected in this presentation for havingsimilar meteorology and photochemical conditions during the EMeRGe campaigns.Significant RO2∗ were observed ca. 55 pptv around Rome and ca. 75 pptv aroundManila. Peroxy radical mixing ratios observed upwind and downwind Rome and Manila arecompared and interpreted according to the different composition of the air masses sampled. [ABSTRACT FROM AUTHOR]