Future changes in surface ozone over the Mediterranean Basin in the framework of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx)

In the framework of the Chemistry and Aerosol Mediterranean Experiment project (ChArMEx, http://charmex.lsce.ipsl.fr ), we study the evolution of surface ozone (O 3 ) over the Mediterranean Basin (MB) with a focus on summertime over the time period 2000–2100, using the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) outputs from 11 models. We consider three different periods (2000, 2030 and 2100) and the four Representative Concentration Pathways (RCP2.6, RCP4.5, RCP6.0 and RCP8.5) to study the changes in the future ozone trend and its budget. We use a statistical approach to compare and discuss the results of the models. We discuss the behavior of the models that simulate the surface O 3 over the MB. The ensemble mean of ACCMIP models simulates very well the annual cycle of surface O 3 . Compared to measured summer surface O 3 datasets, we found that most of the models overestimate surface O 3 and underestimate its variability over the most recent period (1990–2010) when independent observations are available. Compared to the reference period (2000), we found a net decrease in the ensemble mean surface O 3 over the MB in 2030 (2100) for 3 RCPs: −13 % (−36 %) for RCP2.6, −7 % (−22 %) for RCP4.5 and −11 % (−33 %) for RCP6.0. The surface O 3 decrease over the MB for these scenarios is much more pronounced than the relative changes of the tropospheric ozone burden. This is mainly due to the reduction in O 3 precursors and to the NO x -limited regime over the MB. For the RCP8.5, the ensemble mean surface O 3 is almost constant over the MB from 2000 to 2100. We show how the future climate change and the increase in CH 4 concentrations can offset the benefit of the reduction in emissions of O 3 precursors over the MB.