Nitrogen emissions into the atmosphere

Nitrogen emissions into the atmosphere consist mainly of ammonia (NH3) and nitrogen oxides (NOx). In 2022, they comprised 121 million kilograms of ammonia (mainly from agriculture) and 162 million kilograms of NOx (mainly from traffic and industry). Converted into elemental nitrogen (N), this makes a total of 149 million kilograms of nitrogen, of which 100 million kilograms came from ammonia (67 per cent) and 49 million kilograms from NOx (33 per cent). In this article, nitrogen emissions are calculated using the ‘National Emission Ceilings’ (NEC) guidelines (Emissions of Air Pollutants). The NEC definition therefore applies, which means that these figures deviate from those shown in the table ‘Emissions into the air on Dutch territory; totals’.

Ammonia

By far the most ammonia is released by the agriculture sector (about 91 per cent of all ammonia emissions), and is formed when the urea contained in urine in slurry from livestock reacts with the enzyme urease. This process occurs both in the barns where livestock are kept and when slurry is applied to farmland as manure. Cattle account for the majority of ammonia emissions from agriculture (at 53 percent), followed by pigs (17 percent) and poultry (13 percent).

After agriculture, household sources of ammonia are the next largest source, but these are at a much lower level and only make up around 4 percent of total ammonia emissions. Most of this ammonia is released during human breathing and perspiration. Ammonia excreted by domestic pets as well as ammonia in tobacco smoke is also counted in this category. Finally, a very small amount of ammonia is released from traffic or industry (these sources mainly emit NOx).

Nitrogen oxides

Nitrogen oxides (NOx) are released mainly as a product of combustion processes, when oxygen (O2) and nitrogen (N2) in the air react with each other. These combustion processes take place predominantly in vehicles with internal combustion engines and in industrial processes, such as in power plants and blast furnaces. Road traffic is responsible for the largest share of NOx emissions by far, at 34 percent, followed by inland shipping at 13.4 percent. Marine shipping and fishing are not included in this category, but in ‘Other sources’.

Industry and Waste combined make up a share of around 14 percent, while the construction sector contributes around 0.3 percent of NOx emissions. Aviation is also responsible for a relatively small share of total nitrogen oxide emissions (2.1 percent): like shipping, the emissions figures for aviation only include emissions over Dutch territory. These are estimated based on the amount of fuel consumed during the take-off, landing and taxiing of aircraft, along with losses through the evaporation of fuel. NOx emissions during the rest of the flight ¬– beyond Dutch territory – are therefore not counted.

The agriculture sector as a whole is responsible for around 8 percent of total NOx emissions. Agricultural NOx emissions come mainly from the use of heating in greenhouses and mobile (agricultural) machinery. When mobile (agricultural) machinery is excluded, agriculture accounts for 2.6 percent of NOx emissions.