Air quality modelling in the summer over the eastern Mediterranean using WRF-Chem: chemistry and aerosol mechanism intercomparison

We employ the WRF/Chem model to study summertime air pollution, the intense photochemical activity and their impact on air quality over the Eastern Mediterranean. We utilize three nested domains with horizontal resolution of 80 km-16 km-4 km, with the finest grid focusing on the island of Cyprus, where the CYPHEX campaign took place in July, 2014. Anthropogenic emissions are based on the EDGAR HTAP global emission inventory, while dust and biogenic emissions are calculated online. Three simulations utilizing the CBMZ-MOSAIC, MOZART-MOSAIC, and RADM2-MADE/SORGAM gas-phase and aerosol mechanisms are performed. The results are compared with measurements from a dense observational network of 14 ground stations in Cyprus. The model simulates T 2 m , P surf , and WD 10 m accurately, with minor differences in WS 10 m between model and observations at coastal and mountainous stations attributed to limitations in the representation of the complex topography in the model. It is shown that the south-eastern part of Cyprus is mostly affected by emissions from within the island, under the dominant (60 %) westerly flow during summertime. Clean maritime air from the Mediterranean can reduce concentrations of local air pollutants over the region during westerlies. Ozone concentrations are overestimated by all three mechanisms (9 % 3   = 0.29). This might be attributed to the underestimation of NO x concentrations by up to 50 %. For the fine particulate matter (PM 2.5 ), the lowest mean bias (9 μg m −3 ) is obtained with the RADM2-MADE/SORGAM mechanism, with overestimates in sulphate and ammonium aerosols. Overestimation of sulphate aerosols by the RADM2-MADE/SORGAM mechanism may be linked to the heterogeneous SO 2 cloud oxidation. The MOSAIC aerosol mechanism overestimates PM 2.5 concentrations by up to 22 μg m −3 due to a more pronounced dust component compared to the other two mechanisms, mostly influenced by the dust inflow from the global model. We conclude that all three mechanisms are very sensitive to boundary conditions from the global model for both gas-phase and aerosols pollutants, in particular dust and ozone.