Wind flow and photochemical air pollution in Thessaloniki, Greece. Part II: Statistical evaluation of European Zooming Model’s simulation results

In Part I of this paper, the European Zooming Model (EZM) was applied to simulate the wind flow and the pollutant transport and transformation in the Greater Thessaloniki area (GTA) during a day in the midst of the Thessaloniki ’91 Field Measurement Campaign. A quantitative evaluation of the model’s performance is presented here, in Part II. Results of the wind flow and photochemical simulations are compared against observations with the use of appropriate statistical performance measures. Emphasis is given on the intercomparison of the two chemical reaction mechanisms utilized, the compact mechanism KOREM and the more sophisticated mechanism EMEP. High performance evaluation scores are reached regarding wind flow predictions in both coarse and fine grid results. Discrepancies noted mainly in the wind direction are rather difficult to improve as they are attributed to sub-grid variations or to random stochastic fluctuations, which are quite important in light wind situations like the present one. Concerning the photochemical simulations, the statistical evaluation quantified the differences in the performance of the two chemical mechanisms already noted in Part I: Overall, KOREM attains higher scores than EMEP, due to its better performance at the urban sites. EMEP, however, performs better at rural locations and proves its credibility for regional scale simulations.