Regional nitrogen deposition model for integrated assessment of acidification and eutrophication

To complement the continent-scale integrated assessment of emission abatement strategies with regional studies, tools with high resolution are needed. For this purpose, the regional nitrogen transport and deposition model DAIQUIRI using linear transfer matrices, i.e. source-receptor relationships, was developed at the Finnish Environment Institute. The model is based on results of a regional dispersion and deposition model of the Finnish Meteorological Institute (FMI-RM). This paper describes the second phase of model development and validation. The transfer matrices constructed for years 1993 and 1995 were used for generating deposition fields, which were then compared with the results of FMI-RM and continent-scale EMEP model, and with measurements. In addition, the model performance in applications was evaluated: the impacts of regional deposition modelling on exceedances of ecosystem critical loads for acidification were calculated and compared with those using the EMEP model. Both regional models gave comparable results, although some differences existed especially for areas where other land-use types than forest dominate. Also the comparison with measurements showed that estimation of deposition for coastal and sea areas is fraught with uncertainties. For reduced nitrogen, the resolution of the models was insufficient to describe the fine-resolution deposition pattern close to emissions. The comparison with results of the EMEP model, however, showed the ability of regional models to represent the spatial deposition pattern in more detail in areas near emissions. The use of regional modelling resulted in larger estimates of areas at risk of acidification than when using only the continent-scale EMEP model.