What is nitrogen and can we control it?
More nitrogen emissions damage nature. This is why construction and infrastructure projects, for example, will not be granted a permit if they lead to additional emissions. Dutch nitrogen emissions per hectare are the highest in Europe. Several sources are responsible for these emissions. We can improve our knowledge of nitrogen by measuring more frequently and by using new techniques.
New insights into nitrogen sources
View the results of our most recent research using the LOTOS-EUROS chemical transport model
What exactly is nitrogen?
Nitrogen is an element that is found in abundance on earth. The air we breathe consists mainly of nitrogen. This is nitrogen in its pure, non-reactive and harmless form (N2). A small part of the nitrogen on earth and in our air is found in the form of reactive nitrogen. These are chemical compounds which contain nitrogen and are indispensable as nutrients for nature.
However, in excess, reactive nitrogen can have a harmful effect. The main reactive nitrogen compounds that humans emit into the atmosphere are ammonia (NH3) and nitrogen oxides (NOx). These emissions cause a deterioration in air quality before they settle.
When a substance precipitates from the air onto the ground, this is called deposition. Not everything that we emit returns to earth in the same location. Nitrogen oxides (NOx), in particular, can be blown great distances and may settle hundreds of kilometres away. Ammonia (NH3) lands closer to its emission source.
Too much nitrogen causes problems for nature
On 29 May 2019, the Dutch Council of State terminated the Programmatic Approach to Nitrogen (PAS), because the Dutch approach to nitrogen did not sufficiently protect nature. Nitrogen deposition is a major problem for nature management because it leads to soil acidification and eutrophication.
An oversupply of nutrients (eutrophication) then causes an imbalance. Species that need a lot of nitrogen tend to benefit more rapidly from this supply. They then occupy all the space at the expense of other species. So too much nitrogen has a negative effect on biodiversity. This has a negative impact on the insect population and, as a result, on the entire food chain.
In the Netherlands, the critical nitrogen deposition value is exceeded in 72% of terrestrial nature. This is the limit above which there is a risk of a significant deterioration in the quality of nature. In addition, nitrogen oxides and ammonia have a negative effect on air quality, both directly and through their contribution to the formation of particulate matter and ozone (smog).
Gaining control of nitrogen
With a more advanced national monitoring programme, we will be able to measure more accurately and get a better grip on nitrogen:
- Intensification of determining the emission factors for major sources in agriculture, traffic & transport and industry.
- Expansion of ground monitoring network ammonia is the largest contributor to nitrogen problems, but its concentration in the air is measured in less detail than nitrogen oxides. Also, additional measurements of other relevant substances that are currently not measured would be very valuable.
- Satellite data shows? how NH3 and NO2 are distributed over large areas in the Netherlands and neighbouring countries. Using data from the Dutch TROPOMI-satellite instrument, IASI (ESA) and CrIS (NASA), valuable daily measurements can be made over large areas where very few measurements are currently being made.
- New satellite tools can even be used to measure emissions at area level. This way, satellites help us understand where nitrogen comes from and where it goes, and dispersion models can be tested and improved.
- There are benefits to be gained by further developing different modelling systems and making them more compatible with each other, thereby making better use of their individual specialisations.
Facts and figures
In 2017, the Netherlands emitted approximately 132 million kg NH3 and 242 million kg NOx. This translates into 109 million kg of nitrogen (N) from NH3 (60%) and 74 million kg of N from NOx (40%), amounting to 183 million kg of N in total.
If we analyse the total emissions of reactive nitrogen (No), we see that emissions from agriculture are responsible for 61% of total Dutch emissions. In addition, road traffic (15%), industry (9%), non-road traffic (6%) and households and offices (6%) also contribute substantially.
The above percentages are based on the most recent data from the Dutch Emissions Registration. Among the provinces, we see differences in deposition sources.
Uncertainties regarding emissions and nitrogen deposition
Emission and deposition of nitrogen do not often occur in the same location. NOx and NH3 disperse under the influence of weather, where they are (partly) converted into particulate matter before precipitation. The extent of deposition and its consequences are highly location-dependent and depend on, for example, ecosystem type and soil type. There are fundamental uncertainties when determining emissions, atmospheric concentrations and the processes that lead to deposition.
The better we manage to remove these uncertainties, the better we will be able to get a grip on the nitrogen issue. This way, we can better understand the problems and the effects of any measures to be taken.
The uncertainties relate to:
- The quality of the reported emissions of NOx and NH3. These emissions are very rarely measured directly at their source (e.g. in industry); in almost all cases they are estimated by experts (emission factors). In the case of agricultural NH3 emissions, the uncertainty is estimated to be approximately 25%, and for road traffic NOX emissions the uncertainty is estimated to be approximately 12%.
- The extent to which dispersion and deposition are measured. The concentration of NH3 in the air is difficult to measure. In the Netherlands, there are only 7 stations where hourly average concentrations are measured. In addition, there are about 250 locations situated in nature reserves where monthly average observations of concentrations in the air are made. So we are not measuring in very many places and not very often.
- Understanding the processes that lead to deposition. Models are used to calculate total deposition. There are uncertainties in these models. For example, the distances that various substances are transported through the air, or predicting how efficiently different compounds are absorbed by ecosystems and consequently which plants and wildlife is affected. This causes great differences between the models.
 To add up the emissions of NH3 and NOx, the units must be the same. Here we calculate the amount of reactive nitrogen (Nr), therefore NH3 emissions are multiplied by 14/17, and NOx emissions (given as NO2) by 14/46.
 Emission Registration (2018), Dutch emission data for 2017 as officially determined in December 2018.
Mapping nitrogen deposition
Since the Integrated Approach to Nitrogen [Programma Aanpak Stikstof, or PAS] legislation was rejected by the Council of State in 2019, the Netherlands has had to substantially reduce nitrogen emissions. This mainly concerns ammonia (NH3) and nitrogen oxide (NOx) emissions. Too much nitrogen deposition leads to loss of biodiversity. We can take measures and protect nature with the help of measurements and detailed nitrogen deposition maps.
In the Netherlands and Europe, 70% of nature reserves suffer from excessive nitrogen deposition from the atmosphere into the soil. In vulnerable areas, biodiversity is declining due to a combination of eutrophication and acidification. This loss of biodiversity affects ecosystem functions such as:
- food production
- water storage
Major contributors to nitrogen surplus and air pollution are:
We have the knowledge and technology to map out the impact of polluting emissions on ecosystems. We use this to identify the extent to which vulnerable ecosystems are receiving too much nitrogen, for example, in the protected Natura 2000 areas. We get our data from in situ research (where it actually occurs) and satellite monitoring. This helps to reduce uncertainties and determine nitrogen deposition with increasing accuracy.
The cost of reducing nitrogen emissions in Europe amounts to more than 1 billion euros annually. A key question for policy makers and sectors is, therefore, how to avoid nitrogen emissions as efficiently as possible. We provide insight into the origin of nitrogen emissions in a given area. This allows us to identify locally and regionally which measures are most effective, so that we can help policy makers and businesses to answer the question of what measures can be taken to protect these areas. This is how we limit environmental damage and restore ecosystems.
Within the long-term PINETI project, we are producing detailed maps of nitrogen deposition in Germany. We do this with the Umweltbundesamt (UBA) in Berlin, the German National Institute for Public Health and the Environment. With the help of these nitrogen deposition maps, the German government is designing effective policies to reduce nitrogen emissions.
We have published a fact sheet on nitrogen emission and deposition in the Netherlands (pdf). In it we look at different emission sources based on the data currently available. We conclude that there are still many uncertainties in the current data. By collecting much more measurement data of ammonia and nitrogen oxides in the air, we can take more effective measures. We collect this measurement data through the following activities:
- taking measurements with a measurement vehicle at various locations in the Netherlands
- placing measuring instruments at various locations for a prolonged period of time
- satellite data analysis
In the fact sheet on emissions and deposition of nitrogen in the Netherlands, we have not specified the nitrogen emissions from maritime shipping in a number of figures. This has led to a lack of clarity. That is why we are now providing a more detailed explanation of the fact sheet.
Nitrogen emissions from maritime shipping
Statistics Netherlands sets shipping emission at 123.6 kilotons of NOx (nitrogen oxides) in its statistics. The share of inland shipping (27.9 kilotons) is included in the fact sheet as emissions in the Netherlands (see Figure 1. of the fact sheet). NOx emissions from maritime shipping have not been ignored; they have indeed been included in our deposition calculations. However, the emissions there are not identified as ‘Netherlands’ but as ‘Elsewhere in the world’. This is in accordance with the calculation method of the Dutch National Institute for Public Health and the Environment (RIVM).
In order to keep the emitting surface equal to the receiving surface (Dutch territory), maritime shipping emissions have been attributed to “Elsewhere in the world” in the calculations of the import/export ratio.
The share of the total nitrogen deposition in the Netherlands from international shipping is, therefore, included in the category 'Elsewhere in the world'. For this reason, the share from inland shipping is explicitly mentioned.
What is the approximate contribution of maritime shipping to deposition?
NOx emissions from shipping on the North Sea contribute about 2% to the total deposition in the Netherlands. This 2% share is the result of emissions on the entire North Sea. Statistics Netherlands only reports on the Dutch continental shelf (95.8 kilotons for 2017), while the modelling of deposition includes shipping emissions from the entire North Sea.
How can the contribution be so limited?
International shipping is a major source of NOx emissions. But not all NOx emitted in the North Sea reaches the Netherlands. This is only the case when the wind is blowing from in a specific direction. In addition, this concerns the emission of NOx and not NH3. NOx spreads much farther, so some of it will blow over the Netherlands, but will not settle here. NH3 is the nitrogen compound most relevant to issues surrounding the Integrated Approach to Nitrogen [Programma Aanpak Stikstof, or PAS] because it precipitates relatively quickly, i.e., locally.
Opinions are quite divided in the current nitrogen debate. Independent and high-quality soil measurements of the various reactive nitrogen compounds, such as ammonia and nitrogen oxides, can support the debate. Indeed, certainty through statistics. We have a wide range of specialist equipment with which we measure reactive nitrogen in the air. We carry out experimental research with these instruments. We use them to determine:
- the amount of gas coming from a well
- how the gas moves with the wind across the landscape
- how it reacts in the air and forms particulate matter
- where it eventually ends up by dry or wet deposition
Our instruments are useful for the specific measurement purpose of high concentration levels close to a source, but also at very low concentrations at great distances. For example:
- Measuring in and around a source, e.g., poultry barns.
- Measuring near a source, e.g., NOx (nitrogen oxides) measurements near a road.
- Measuring at a great distance, where reactive nitrogen causes problems. For example, we measure the spread of gases and particles above a forest. There, they come into contact with the stomata on leaves.
In the Netherlands, we are currently the only independent research organisation with infrared laser spectrometers. We use them to measure, for example, ammonia and NOx at ppb level (one part per billion air particles) with several measurements per second. As a result, we can visualise a cloud of gas downwind of a source and calculate the emissions from that source. We can also count how many ammonia or nitrous oxide particles go up and down above a fertilised pasture and determine the emission of a field from this difference.
For the measurement of a long-term time series, we use the miniDOAS, an open-path measuring system developed by the RIVM. This instrument requires no suction tubes or dust filters, making it extremely suitable for measuring the sticky ammonia gas in the air. A version of this instrument is now installed at the Sorbonne, measuring ammonia concentrations in the heart of Paris. We built it together with Admatec from Alkmaar.
We use measurements that look up from the ground at the concentrations of ammonia (NH3) in the column of air above to calibrate satellite data. The satellites supplement the measurements with valuable measurements in areas where there are no ground stations.
In the atmosphere, the ammonia, but also the NOx from traffic, reacts with other compounds in the air to form particles. We also have the measuring instruments to map out ammonium nitrate and ammonium sulphate aerosols. This allows us to understand the contribution of ammonia and NOx sources to the formation of particulate matter.
Costly and complicated instruments are not always necessary. A monthly average concentration of NO2 (nitrogen dioxide) can also be determined with a simple adsorption tube fixed to a lamppost. In between such inexpensive measurements and the aforementioned high-quality instruments, we have filter tubes. They suck in air, capture gases on coated tubes, and collect particles on a filter.
We are also working hard to develop medium- and low-cost sensors to measure the reactive nitrogen components online at several points simultaneously. For this purpose, we are also seeking to collaborate with companies, knowledge institutes, and universities.
For decades, the Netherlands was a scientific leader in the field of reactive nitrogen compounds, as well as in the development of measurement methods and instruments. However, nitrogen research in our country has been on the back burner for the last decade. As a result, the development of measuring methods and instruments is much slower than in the 1980s and 1990s. The time has now come to pick up where we left off. With new techniques and electronics, we will provide answers to mostly old, but as yet unanswered nitrogen questions.
Martijn SchaapFunctie:Researcher air quality
Major environmental challenges of the 21st century relate to the composition of our atmosphere. Exposure to pollutants such as particulate matter is associated with significant health impacts. Deposition of atmospheric reactive nitrogen causes a loss of biodiversity in ecosystems through eutrophication.
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