Comparison of Airborne Peroxy Radical Measurements with MECO(n) model simulation during EMeRGe in Europe

Observations of tropospheric peroxy radicals are a key point for interpretation of the processing and transformation of polluted outflows from major populated centres (MPCs). A series of European MPCs are investigated by the project EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional and Global scales). With this objective two airborne campaigns using the research platform HALO (High Altitude and LOng range aircraft) were carried out over Europe in summer 2017 and over east Asia in the intermonsoon period in 2018. The Institute of Environmental Physics (IUP) in Bremen (Germany) participated in both EMeRGe campaigns with the airborne measurement of the total sum of peroxy radicals, RO2*, by using the home made PeRCEAS instrument based on the combination of the PERCA (peroxy radical chemical amplification) and CRDS (cavity ring down spectroscopy) techniques. One of the main purposes of the campaigns was the investigation of the characteristics and chemical transformation of MPC outflows at the local and regional scales.During the EMeRGe campaign in Europe, air masses of different photochemical activity were measured, where RO2* mixing ratios up to 100pptv being observed. In the present study the RO2* observations for six measurement flights of EMeRGe in Europe have been compared with RO2 (here defined as the sum of HO2 + CH3O2 + ISOOH + CH3CO3 + CH3COCH2O2) simulated by using the MECO(n) model.MECO(n) (MESSy-fied ECHAM and COSMO models nested n times), is a global/regional chemistry-climate model developed by the MESSy consortium, which couples on-line the global chemistry-climate model EMAC with the regional chemistry-climate model COSMO-CLM/MESSy. The same anthropogenic emission inventory (EDGAR 4.3.1) as well as the same solver for chemical kinetics, involving complex tropospheric and stratospheric chemistry, are applied in EMAC and COSMO-CLM/MESSy.Overall, the agreement between the measurements and model is reasonable for RO2* observations below 40 pptv. Events with higher mixing ratios seem not to be well reproduced by the model but underestimated. Further details on the modelling and the result of the comparison will be presented.