Wet deposition of ammonium, nitrate and sulfate in the Netherlands over the period 1992–2008

We present measurements of wet deposition of ammonium, nitrate and sulfate in the Netherlands over the period 1992–2008. These data series are obtained from the Dutch National Precipitation Chemistry Monitoring Network which consists of 11 monitoring stations which are homogeneously spread over the Netherlands. These long-term measurements allow for a trend analysis over this period, which are to a large extent not influenced by the year to year variations in meteorological circumstances. It is shown that the downward trend of ammonium, nitrate and sulfate wet deposition over the period 1992–2008 are statistically significant: the wet deposition in the Netherlands decreased in the period 1992–2008 by 37% for ammonium, 28% for nitrate and 59% for sulfate. A comparison between the measurements and emissions are made in order to check whether the emissions show similar downward trends. Subsequently a comparison is made between measured and calculated wet deposition fluxes. These calculation results were performed with the Operational Priority Substances (OPS-model). The trends in both the emissions and the calculated wet deposition fluxes show good agreement for all three measured components. It is therefore concluded that the downward trends of the wet deposition fluxes are a direct effect of the decrease of emissions. Finally, it is shown that the relative downward trend of the wet deposition fluxes of sulfate in the Netherlands shows a large-scale structure with a gradient running from east to west. A similar pattern is seen in the simulations performed with the OPS-model.

► Wet deposition levels of sulfur and nitrogen in the Netherlands are presented.
► Both components have a downward trend over the period 1992–2008.
► These downward trends are statistically significant.
► The downward trends are the result of emission reduction of the precursors.