Impact of vertical and horizontal resolutions on chemistry transport modelling

This paper presents the main results of two specific studies related to the sensitivity of spatial resolution on chemistry transport modeling. The horizontal scale is addressed by simulating the air quality in Europe for the full year 2009 at 50 and 8 km resolutions on a very high performance computing infrastructure. An additional 2 km resolution was performed on a smaller period to assess the added value of a very high horizontal resolution during the air pollution outbreak of January 2009 when particulate and nitrogen dioxide levels reached alert levels. We reveal small scale air pollution patterns that highlight the contribution of city plumes to background air pollution levels. The influence of the vertical resolution on air pollutant concentrations near the surface is studied. The results are discussed in terms of differences on surface concentrations between the reference case and an improved resolution. Adding a point close to the surface appears to be important mainly for high nocturnal concentrations in very stable boundary layers.