Operational mapping of atmospheric nitrogen deposition to the Baltic Sea O. Hertel, C. Ambelas Skjøth, J. Brandt, J. H. Christensen, L. M. Frohn, and J. Frydendall National Environmental Research Institute, Department of Atmospheric Environment, P.O. Box 358, Frederiksborgvej 399, 4000 Roskilde, Denmark
Abstract. A new model system for mapping and forecasting nitrogen deposition to the Baltic Sea has
been developed. The system is based on the Lagrangian variable scale transport-chemistry
model ACDEP (Atmospheric Chemistry and Deposition model), and aims at delivering
deposition estimates to be used as input to marine ecosystem models. The system is tested by
comparison of model results to measurements from monitoring stations around the Baltic Sea.
The comparison shows that observed annual mean ambient air concentrations and wet
depositions are well reproduced by the model. Diurnal mean concentrations of
NHx (sum of NH3 and NH4+) and
NO2 are fairly well reproduced, whereas concentrations of total nitrate
(sum of HNO3 and NO3-) are somewhat overestimated. Wet depositions of nitrate and
ammonia are fairly well described for annual mean values, whereas the discrepancy is high
for the monthly mean values and the wet depositions are rather poorly described concerning
the diurnal mean values. The model calculations show that the annual atmospheric nitrogen
deposition has a pronounced south--north gradient with depositions in the range about
1.0 T N km-2 in the south and 0.2 T N km-2 in the north. The results show that in
1999 the maximum diurnal mean deposition to the Danish waters appeared during the summer in
the algae growth season. For the northern parts of the Baltic the highest depositions were
distributed over most of the year. Total deposition to the Baltic Sea was for the year 1999
estimated to 318 kT N for an area of 464 406 km2 equivalent to an average deposition of
684 kg N/km2.
Citation: Hertel, O., Ambelas Skjøth, C., Brandt, J., Christensen, J. H., Frohn, L. M., and Frydendall, J.: Operational mapping of atmospheric nitrogen deposition to the Baltic Sea, Atmos. Chem. Phys., 3, 2083-2099, doi:10.5194/acp-3-2083-2003, 2003.