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Volume 18, issue 3 | Copyright

Special issue: The community version of the Weather Research and Forecasting...

Atmos. Chem. Phys., 18, 1555-1571, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Feb 2018

Research article | 02 Feb 2018

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

George K. Georgiou1, Theodoros Christoudias2, Yiannis Proestos1, Jonilda Kushta1, Panos Hadjinicolaou1, and Jos Lelieveld3,1 George K. Georgiou et al.
  • 1Energy, Environment and Water Research Center, The Cyprus Institute, Nicosia, Cyprus
  • 2Computation-based Science and Technology Research Centre (CaSToRC), The Cyprus Institute, Nicosia, Cyprus
  • 3Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany

Abstract. 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 resolutions of 80, 16 and 4km, 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 T2 m, Psurf, and WD10 m accurately, with minor differences in WS10 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% ≤ NMB ≤ 23%) with the smaller mean bias (4.25ppbV) obtained by the RADM2-MADE/SORGAM mechanism. Differences in ozone concentrations can be attributed to the VOC treatment by the three mechanisms. The diurnal variability of pollution and ozone precursors is not captured (hourly correlation coefficients for O3 ≤ 0.29). This might be attributed to the underestimation of NOx concentrations by local emissions by up to 50%. For the fine particulate matter (PM2.5), the lowest mean bias (9µgm−3) is obtained with the RADM2-MADE/SORGAM mechanism, with overestimates in sulfate and ammonium aerosols. Overestimation of sulfate aerosols by this mechanism may be linked to the SO2 oxidation in clouds. The MOSAIC aerosol mechanism overestimates PM2.5 concentrations by up to 22µgm−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 aerosol pollutants, in particular dust and ozone.

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We investigate the impact of the choice of gas-phase and aerosol mechanisms, on the simulated summertime concentrations of several pollutants over the eastern Mediterranean, using the WRF-Chem model. The selection of mechanisms significantly affects ozone and fine particulate matter concentrations, and to a lesser extent other gaseous pollutants (NOx, CO). Meteorological components are also affected by the choice of mechanisms due to the interaction of aerosols with radiation.
We investigate the impact of the choice of gas-phase and aerosol mechanisms, on the simulated...