Air pollution forecasting from regional to urban street scale––implementation and validation for two cities in Denmark

Abstract

An operational air pollution forecast model system, THOR, has been developed. The system is used for 3-days forecasting, monitoring and traffic and/or emission reduction scenarios. The model system includes several models capable of calculating air pollution concentrations at different spatial scales, ranging from European scale over urban background scale down to urban street scale. When coupling models covering such different scales, it is possible to include contributions both from local, near-local and non-local emission sources in order to describe the air quality at a specific location––e.g. in a street canyon. The different air pollution models are driven by a numerical weather forecast model. Operational three days air pollution forecasts are produced four times every day. The system can, in principle, be applied for any city in Europe. Currently the regional model has been implemented for the whole of Europe and the urban models for two major cities in Denmark; Copenhagen and Aalborg. The individual models in the system will be shortly described and typical model results will be shown. The model system has been operational since August 1998 and is continuously being validated against measurements from the Danish urban monitoring network. Results from the evaluation of the system performance for the city of Aalborg and comparisons with results for the city of Copenhagen will be presented. The results show that the street pollution model has quite similar performance for the two cities. However, a difference is seen in the performance of the urban background model for the two cities, which is probably due to the difference in the spatial resolution of the urban emission data.