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Construction the European aerosol nitrate concentration field from experimental data
Schaap, M.; Brink, H.M. ten; Müller, K.
Gepubliceerd door: Publicatie datum:
ECN SF 1-6-2001
ECN publicatienummer: Publicatie type:
ECN-RX--01-033 Artikel wetenschap tijdschrift
Aantal pagina's:

Gepubliceerd in: Submitted in shortened form to: Atmospheric Environment (), , , Vol., p.-.

We report on the construction of the aerosol nitrate concentration field in Europe from measured data, The central hurdle in this procedure was the unknown quality of the data for this semi-volatile component due to a range of artefacts occurring during sampling. The first step in this study was therefore a search for (long-term) data obtained with sampling methods which do not suffer from artefacts, viz. denuder-filter combinations. Because of the paucity of such data, values obtained via sampling with simple filters were critically analysed. We start the reporting with a general review of filter types in use in Europe and the associated artefacts. It could be demonstrated that the largest artefact with inert filters (Teflon and Quartz) in Europe is the evaporation of ammoniumnitrate and that, hence, the reported concentrations arelower values. Next, data from ?total-nitrate? filters, i.e. filters that collect both aerosol nitrate and nitric acid gas, were critically analysed. The contribution of the gaseous compound was corrected for on the basis of concentration data from campaigns at the measuring sites or at nearby locations.? The distances over which nitrate concentrations at the various stations correlate were then analysed and it was found that in the winter half-year the correlation length was sufficiently long to warrant interpolation of the point data. In addition, it was found that sampling artefacts are also minimal in that period of the year. The nitrate concentration field as obtained from interpolation of the nitrate-data in the period 1994-1997 was successfully validated against intermediate point data from shorter lasting campaigns. The field has a large area of high nitrate concentrations ranging from southern England over continental West-Europe into Poland, with concentrations of nitrate exceeding 5 µg m-3. Strong arguments are provided that the nitrate is predominantly present in the fine aerosol fraction (PM2.5), as ammonium nitrate. To the north nitrate concentrations range from 2.5 µg m-3 in Sweden to less than 0.5 µg.m-3 in mid-Scandinavia. To the east and west of Central Europe the maximum nitrate concentration trails off in a more gradual way. It was inferred that the concentration of nitrate in winter in Europe,north of the Alps, with the exception of France (from which country no data could be found), is at least 60% higher than that of sulphate. It should further be mentioned that in the PO-Valley ammonium nitrate levels are as high as those in West-Europe. Since there are also strong indications that the nitrate is in the submicron fraction it contributes in a similar way to aerosol light-scattering and visibility impairment as sulphate.

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