Currently, atmospheric chemistry and transport models (ACTMs) used to assess impacts of air quality, applied at a European scale, lack the spatial resolution necessary to simulate fine-scale spatial variability. This spatial variability is especially important for assessing the impacts to human health or ecosystems of short-lived pollutants, such as nitrogen dioxide (NO<sub>2</sub>) or ammonia (NH<sub>3</sub>). In order to simulate this spatial variability, the Air Quality Re-gridder (AQR) model has been developed to estimate the spatial distributions (at a spatial resolution of 1 × 1 km<sup>2</sup>) of annual mean atmospheric concentrations within the grid squares of an ACTM (in this case with a spatial resolution of 50 × 50 km<sup>2</sup>). This is done as a post-processing step by combining the coarse-resolution ACTM concentrations with high-spatial-resolution emission data and simple parameterisations of atmospheric dispersion. The AQR model was tested for two European sub-domains (the Netherlands and central Scotland) and evaluated using NO<sub>2</sub> and NH<sub>3</sub> concentration data from monitoring networks within each domain. A statistical comparison of the performance of the two models shows that AQR gives a substantial improvement on the predictions of the ACTM, reducing both mean model error (from 61 to 41 % for NO<sub>2</sub> and from 42 to 27 % for NH<sub>3</sub>) and increasing the spatial correlation (<i>r</i>) with the measured concentrations (from 0.0 to 0.39 for NO<sub>2</sub> and from 0.74 to 0.84 for NH<sub>3</sub>). This improvement was greatest for monitoring locations close to pollutant sources. Although the model ideally requires high-spatial-resolution emission data, which are not available for the whole of Europe, the use of a Europe-wide emission dataset with a lower spatial resolution also gave an improvement on the ACTM predictions for the two test domains. The AQR model provides an easy-to-use and robust method to estimate sub-grid variability that can potentially be extended to different timescales and pollutants.