Pergamon

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S e s s i o n 6 A - M a r i n e a e r o s o l s

INFLUENCE OF AEROSOL FORMATION ON NITROGEN DEPOSITION IN A COASTAL REGION USING THE METRAS/SEMA MODEL

LAURA KLEIN 1, HEINKE SCHLUNZEN 1, KNUT VON SALZEN 2

1 Meteorologisches Institut, Universit~it Hamburg, Bundesstr. 55, 20146 Hamburg

2 Canadian Centre for Climate Modelling and Analysis, University of Victoria, P.O. Box 1700, STN CSC, Victoria, BC VSW 2Y2

,4eloso/&'i \H. 31, Suppl. 1, pp. $542 $543,2000

Keywords: coastal aerosol, nitrogen deposition

INTRODUCTION

Coastal environments face air quality issues which are complex and unique. Of particular interest is the atmospheric nitrogen input to coastal waters. It has been recognised that the atmosphere provides a significant nitrogen input to ocean regions, particularly those downwind of major industrial and populated areas. It is estimated that 27% of the total nitrogen input to the North Sea is from direct atmospheric deposition to the water only and does not include the deposition to the watershed which is eventually runoff into the sea (Duce, 1998), It is important to understand the interaction between the urban atmosphere, the coastal atmosphere, and secondary aerosol development in order to target the pollutants which are major precursors. This paper addresses the influence of aerosol formation on nitrogen deposition in the southern North Sea.

METHOD

The mesoscale model METRAS (Schltinzen, 1990; Schltinzen et al., 1996) will be applied to simulate coastal atmospheric phenomena including the nitrogen transport and the composition of coastal aerosol. METRAS is a multi-layer dispersion model which can generate three-dimensional meteorology fields. This model is coupled with the Chemical Transport Model (MECTM) which includes a gas phase chemistry (Stockwell et al., 1997) and the aerosol model SEMA (von Salzen, 1997, von Salzen and Schltinzen, 1999a, 1999b). SEMA combines a thermodynamic equilibrium approach with a kinetic approach to predict the condensation and evaporation at the surface of the aerosol. This model has been applied in previous studies simulating inorganic aerosols in the coastal environment (von Salzen and Schlttnzen, 2000). SEMA uses a sectional algorithm approach to solve the resulting equations. At present, the aerosol model is limited to wet aerosols.

The above mentioned models have been prepared for application in the area of the North Sea to simulate the summer 1998 measuring campaign of the ANICE project. The model area was chosen to encompass the observation sites at Meetpost Noordwijk (The Netherlands) and Weybourne Atmospheric Observatory (Great Britain). After reviewing the wind trajectories, specific days from the 1998 field campaign were chosen when there was connecting flow between t.he two monitoring stations, June 16 - 20. A review of weather charts showed that there were no major weather systems moving through the region during that period. The output from the German Weather Service's forecast model, the Deutschland Model (DWD, 1998) was used to nudge the meteorology of METRAS.

The METRAS/MECTM model system has been run. The concentration and deposition fields are analysed and compared with measured data.

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MODEL RESULTS AND COMPARISON WITH OBSERVATION DATA

The first step in the comparison process was to analyse the meteorological data output from METRAS against observations. It is important for the meteorology simulations to be good because the level of accuracy will be reflected in the chemistry runs and increases the confidence in the final results. The METRAS results agree well with measured data (Klein et al, 2000).

The coupled METRAS/MECTM model was run for a period of 5 days, from June 16 to June 20, 1998. It is expected that the inclusion of an aerosol phase will cause a reduction in the dry deposition of ammonia and nitric acid. This reduction will change the spatial distribution and total amounts ofNH4 + and NO 3.

ACKNOWLEDGMENT

This work was funded by the European Commission and the University of Hamburg. The authors are responsible for the contents of this publication. ANICE is part of ELOISE and is supported by EC DG XII, contract ENV4-CT97-0526. Data from the German Weather Service (DWD) were used in the model runs and the model evaluations.

REFERENCES

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Duce, R. (1998) The input of atmospheric chemicals to the ocean. WMO Bulletin. 47, 51-60. Klein, L., C.J. Lenz, and K.H. Schlfinzen (2000). Comparison of Model vs. Observations: ANICE

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coastline with tidally flooded mudflats. Beitr. Phys. Atmosph. 63 : 243 - 256. Schlthazen K.H., Bigalke K., L~pkes C., Niemeier U. and von Salzen K. (1996). Concept and

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