Deposition of nitrogen compounds

Nitrogen deposition refers to the processes by which nitrogen in reactive nitrogen compounds in the air is deposited onto soil and into water. The nitrogen gas (N2) that is naturally present in the air is inert and remains in the atmosphere; deposition does not apply to that form of nitrogen.

Reactive nitrogen compounds are released into the air through emissions. The main compounds involved are ammonia (NH3) and nitrogen oxides (NOx). All the ammonia and nitrogen oxides emitted by various sources (agriculture, traffic, industry) eventually end up back in the land or water. Some of the nitrogen is deposited in rain (wet deposition), while the remainder is deposited through the action of gravity (dry deposition). Ammonia can react in the air or in water to form ammonium (NH4+).

The RIVM (National Institute for Public Health and the Environment) uses the Operational Priority Substances (OPS) model in order to simulate nitrogen dispersion and deposition.

About two thirds of all nitrogen (N) precipitated by deposition is NHy (NH3 and NH4+ together), and the remaining third is NOx. Around 29 percent of the nitrogen deposited on Dutch territory comes from abroad, most of it emitted in Germany, followed by Belgium. The deposition of nitrogen emitted by sources in the Netherlands (71 percent) comes mainly from agriculture and traffic. The share from abroad may seem high, but in fact four times as much nitrogen emitted in the Netherlands is deposited in other countries as the other way around. In addition to nitrogen emitted by agriculture and traffic in the Netherlands, some of which is deposited just across the border, maritime shipping also plays a major role.

Highest nitrogen deposition in built-up areas and forests

Where is the most nitrogen deposited? The RIVM’s Operational Priority Substances (OPS) model simulates both wet and dry deposition. Deposition depends firstly on the type of nitrogen compound involved (ammonia or nitrogen oxides). Secondly, the distance from the emission source plays a role: most nitrogen stays close to the source, and because there are so many emission sources (agriculture, traffic, industry) nitrogen deposition is distributed across the whole country. The roughness of the surface on which the nitrogen lands is the third factor that determines the degree of deposition. Most nitrogen per hectare is deposited in built-up areas, followed by forest areas. The least nitrogen per hectare is deposited on water.