Downscaling of the EMEP model using UEMEP: where scales meet

Regional scale air quality models are regularly used for assessing health impacts over country or continental scales. However, these models lack sufficient resolution to represent pollution gradients near sources, particularly in the case of road traffic emissions, and are based mostly on top down emission inventories. From the regional modelling perspective it is therefore desirable to down scale gridded concentrations to a resolution that are sufficient to resolve these sources, approximately 50 m, for improved exposure assessment. At the same time local scale models, often based on Gaussian plume parameterisations and using bottom up emissions inventories, are also regularly applied for health impact assessments but are rarely used beyond the city scale. In this paper a methodology for downscaling regional scale concentrations from the EMEP/MSC-W model to local scales is presented, uEMEP (urban EMEP). The methodology requires bottom up emission proxy data, which is often incompatible with the top down inventories, for the redistribution of gridded concentrations. Results are presented for Norway and The Netherlands and the problems encountered when regional and local scales meet are discussed.