Operational mapping of atmospheric nitrogen deposition to the Baltic Sea

[摘要] A new model system for mapping and forecasting nitrogen deposition to the Baltic Sea hasbeen developed. The system is based on the Lagrangian variable scale transport-chemistrymodel ACDEP (Atmospheric Chemistry and Deposition model), and aims at deliveringdeposition estimates to be used as input to marine ecosystem models. The system is tested bycomparison of model results to measurements from monitoring stations around the Baltic Sea.The comparison shows that observed annual mean ambient air concentrations and wetdepositions are well reproduced by the model. Diurnal mean concentrations ofNH_x (sum of NH₃ and NH₄⁺) andNO₂ are fairly well reproduced, whereas concentrations of total nitrate(sum of HNO₃ and NO₃^-) are somewhat overestimated. Wet depositions of nitrate andammonia are fairly well described for annual mean values, whereas the discrepancy is highfor the monthly mean values and the wet depositions are rather poorly described concerningthe diurnal mean values. The model calculations show that the annual atmospheric nitrogendeposition has a pronounced south--north gradient with depositions in the range about1.0 T N km^-2 in the south and 0.2 T N km^-2 in the north. The results show that in1999 the maximum diurnal mean deposition to the Danish waters appeared during the summer inthe algae growth season. For the northern parts of the Baltic the highest depositions weredistributed over most of the year. Total deposition to the Baltic Sea was for the year 1999estimated to 318 kT N for an area of 464 406 km² equivalent to an average deposition of684 kg N/km².

[学科分类] 大气科学