ETC/ATNI Report 2021/20: European-wide city level air quality mapping. Evaluation of the current mapping methodology with respect to the level of cities and NUTS3 units and suggestions for future.

The report examines city-level mapping at the European scale, with the aim to provide consistent spatial information at NUTS3 and city levels across Europe. It introduces the population-weighted concentration based on the mapping results as a potential new approach for the city ranking. It also suggests several possibilities of future development towards the European-wide city level mapping in a fine resolution. The report evaluates current mapping methodology with respect to city- and NUTS3-levels mapping across Europe. It states that the current mapping can be used at the city and the NUTS3 levels, despite a mild smoothing effect at locations of the measurement stations. However, it suggests a post-processing correction based on the mapping residuals. A potential new approach for the city ranking have been examined, namely the population-weighted concentration based on the mapping results. While the averaged measurement data from the background stations (as used in the current city ranking) provides a superior information for the whole city in general, the population-weighted concentration also well represents the whole city and gives a consistent information for all cities, including those without station measurements. Next to this, alternative treatments of rural and urban stations has been evaluated. If the urban traffic areas should be better represented in the final maps, an increased map resolution is recommended. Several possibilities of future development towards the European-wide city level mapping in a fine resolution have been suggested, namely exploitation of a high-resolution model output in the existing methodology, geostatistical downscaling of the existing spatial maps using fine-resolution proxy datasets and exploitation of existing low-cost sensor networks.OCP/EEA/CAS/21/005-ETC H