High-resolution air quality simulation over Europe with the chemistry transport model CHIMERE

Abstract. A modified version of CHIMERE 2009, including new methodologies in emissions modelling and an urban correction, is used to perform a simulation at high resolution (0.125° × 0.0625°) over Europe for the year 2009. The model reproduces the temporal variability of NO₂, O₃, PM₁₀, PM_2.5 better at rural (RB) than urban (UB) background stations, with yearly correlation values for the different pollutants ranging between 0.62 and 0.77 at RB sites and between 0.52 and 0.73 at UB sites. Also, the fractional biases (FBs) show that the model performs slightly better at RB sites than at UB sites for NO₂ (RB = −33.9%, UB = −53.6%), O₃ (RB = 20.1%, UB = 25.2%) and PM₁₀ (RB = −5.50%, UB = −20.1%). The difficulties for the model in reproducing NO₂ concentrations can be attributed to the general underestimation of NO_x emissions as well as to the adopted horizontal resolution, which represents only partially the spatial gradient of the emissions over medium-size and small cities. The overestimation of O₃ by the model is related to the NO₂ underestimation and the overestimated O₃ concentrations of the lateral boundary conditions. At UB sites, CHIMERE reproduces PM_2.5 better than PM₁₀. This is primarily the result of an underestimation of coarse particulate matter (PM) associated with uncertainties in secondary organic aerosol (SOA) chemistry and its precursor emissions (Po valley and Mediterranean basin), dust (south of Spain) and sea salt (western Europe). The results suggest that future work should focus on the development of national bottom-up emission inventories including a better account for semi-volatile organic compounds and their conversion to SOA, the improvement of the CHIMERE urban parameterization, the introduction into CHIMERE of the coarse nitrate chemistry and an advanced parameterization accounting for windblown dust emissions.