A Model Evaluation Strategy Applied to Modelling of PM in the Helsinki Metropolitan Area

We have developed a deterministic urban scale dispersion modelling system further by adding a road dust suspension model. The system includes both vehicular exhaust emissions and suspended road dust. The modelling system was combined with a regional scale chemical transport model for calculations of concentrations in an urban area for the year 2008, and for the year 2010 measured regional background concentration was used. The time series' were modelled for a spatial area more extensive than before using the FORE road dust suspension model. The predictions were compared against observed concentrations of PM2.5 and PM10. The use of the index of determination (r(2)) is discussed. We criticize the use of r(2) alone as well as in addition to an index of agreement-type measure of agreement, and review the underlying data assumptions for the use of both measures. We then suggest a strategy to develop model evaluation statistical understanding, practice and nomenclature.