Air quality forecasts at kilometer scale grid over Spanish complex terrains

Abstract

Abstract. CALIOPE-AQFS represents the current state-of-the-art in air quality forecasting systems running at high resolution over high performance computing platforms. It provides 48 h forecast of main pollutants over Spain at 4 km horizontal resolution, and over the most populated areas with complex terrains in Spain (Barcelona, Madrid and Andalucia domains) at 1 km. Increased horizontal resolution from 4 km to 1 km over the aforementioned domains leads to finer texture and more realistic concentration maps, justified by the increase of NO2/O3 spatial correlation coefficients from 0.79/0.69 (4 km) to 0.81/0.73 (1 km). High resolution emissions using the bottom-up HERMESv2.0 model are essential to improve the model performance when increasing resolution at urban scale, but it is not sufficient. Decreasing grid spacing does not reveal the expected improvement on hourly statistics, decreasing NO2 bias only in ~ 2 μg m−3 and increasing O3 bias in ~ 1 μg m−3. The grid effect is less pronounced for PM10 because part of its mass consists of secondary aerosols which are less affected by a decreasing grid size in contrast to the locally emitted primary components. The resolution increase has the highest impact over Barcelona, where air flow is mainly controlled by mesoscale phenomena and a lower PBL. Despite the merits and potential uses of the 1 km simulation, the limitations of current model formulations do not allow confirming their expected superiority close to highly urbanized areas and large sources. Future work should combine high grid resolution with techniques that decrease subgrid variability and models that consider urban morphology and thermal parameters.