In the Netherlands, nearly all wet nitrogen deposition occurs in the form of ammonium and nitrate. Such is the main conclusion from a study of non-routinely measured forms of nitrogen in precipitation. This means that contributions to total nitrogen deposition from substances other than those related to nitrogen oxides and ammonia are likely to be negligible.
Traditionally, the calculation of nitrogen deposition was based on results from measurements of ammonia and nitrate concentrations in precipitation. However, the literature indicates that nitrogen components other than ammonia and nitrate could add non-negligible amounts to wet nitrogen deposition.
The most recent research in the Netherlands on this subject dated back more than twenty years. Therefore, research was carried out in 2006 and 2008 on the occurrence of organic nitrogen compounds in Dutch precipitation. Next to the classical components ammonia and nitrate, the research was directed to total nitrogen, amines, urea and amino acids.
Amino acids and amines were not found; the amount of total nitrogen in precipitation, on average, did not differ significantly from the total of the nitrogen in ammonia and nitrate. However, in 50 per cent of the cases, we did find urea, and its contribution to wet deposition could average out at 2 per cent. This would bring the maximum contribution of urea to the total nitrogen deposition to 1 per cent. This contribution, for all practical purposes, can be considered negligible.
Main conclusions of the research are:
- Practically all wet deposition of nitrogen in the Netherlands consists of ammonia and nitrate.
- The contribution of substances other than ammonia or nitrogen oxide derivatives, in the Netherlands, are likely to be negligible.