A simple and fast method to downscale chemistry transport model output fields from the regional to the urban/district scale

For policy applications, the need to improve the resolution of environmental variables is crucial. Air pollution assessment indeed requires the use of air pollutant concentration fields at a high resolution, to better evaluate the exposure of citizens. In this paper, we propose a fast proxy-based downscaling strategy, to downscale air quality modelling results using the fraction of the pollutant concentration influenced by precursor emissions in a given cell. The approach combines in an additive way (i) a classically interpolated background pollutant fraction, with (ii) a proxy-based concentration derived from the emissions. The proxy-based pollutant fraction is spread over the high resolution mesh into the surrounding cells with a Gaussian approach to account for diffusion effects. The evaluation of our approach against observations shows its relevance to create reliable air pollution concentration fields at a higher resolution, starting from a coarse resolution modelling results. [Display omitted] •A downscaling method is developed to create high resolution maps of pollutant concentrations.•The method is evaluated against observations over Europe.•A general improvement is observed in most places, largely driven by an improvement of the bias.•The code is fast and produces a top-down high-resolution inventory, as a side product.