How is nitrogen measured and how reliable is it?

According to the cabinet, nitrogen emissions must be halved by 2030 to protect vulnerable nature. But many farmers and some politicians are critical of how nitrogen emissions and precipitation are measured. In this story, we explain how it works.

Although we can’t see or smell it, nitrogen is all around us. When we talk about nitrogen reduction, we are talking about gas emitted by traffic, industry and livestock. According to the government, the emission of nitrogen must be drastically reduced, especially near vulnerable Natura 2000 areas. Sometimes even by 70 percent, as in De Groote Peel. In this way, these natural areas must be preserved.

But if you can’t see and smell nitrogen, how do you measure it? For that, we have to be at RIVM. This body measures and calculates how much nitrogen is emitted and how much lands on Dutch soil.

How to measure nitrogen

There are 43 nitrogen oxide and 6 ammonia measuring stations spread throughout the Netherlands. Nitrogen researcher Marloes Penning de Vries explains in a video from the University of the Netherlands how ammonia is measured. UV light shines on a mirror 50 meters away in the 6 locations. Ammonia absorbs light. The amount of reflected light is analyzed. This shows how much ammonia is in the air. The nearest measuring station is a stone’s throw from our province in Vredepeel in Limburg.

A handful of installations is obviously not enough. That is why there are an additional 300 measuring points in nature reserves. These are tubes with filters that suck in air. Ammonia stays on the filter, says Penning de Vries. Scientists look at how much nitrogen is in a laboratory. Special satellite images map the rest of the country.

Nitrogen also comes down through rain. RIVM therefore investigates the composition of raindrops. And then there is another measurement method. “Nature lends a hand,” says Penning de Vries. “Some mosses do not like nitrogen at all, while others do. So if you count how many of one and the other type of lichen there are in different places in the Netherlands, you know how much ammonia has been in the air.”

How to calculate nitrogen

However, it is not possible to map the exact amount of nitrogen in the air and what settles on the ground. According to the RIVM, this costs too much money and is practically impossible. To provide a national picture, RIVM works with a few calculation models. Computers make calculations based on data that is entered. Partly on the basis of this, it is investigated whether there is still room for nitrogen to, for example, build new homes or livestock barns.

Among other things, RIVM looks at how many sources of nitrogen emissions there are. For example: how many kilometers of asphalt, cars and factories are there. But also: how many cows there are, what they eat, what kind of barns there are, how the manure is stored and spread. RIVM also takes into account wind direction, temperature and how much moisture there is in the air. All of this affects where nitrogen ends up. Because the weather changes all the time, according to Penning de Vries, it also affects the accuracy of the calculations.

“The model is compared again and again with all the different measurements. The regional measurements correspond to what the model calculates,” says the researcher in the video. “This shows that ammonia emissions urgently need to be reduced.”

Justified criticism of nitrogen models?

Many farmers and some politicians criticize the way in which RIVM maps nitrogen emissions and landings. For example, BBB, JA21 and a large part of VVD supporters believe that more measurements should be taken. And less has to be calculated through models.

The RIVM rejected this criticism. A commission of inquiry concluded in 2020 that the quality of nitrogen methods, models and data is adequate to good. Calculations are too detailed for individual emitters and therefore not appropriate. But on a large scale this is the case. The chairman of that committee, Leen Hordijk, still supports this. He told Nieuwsuur in June that the Netherlands measures nitrogen ‘using the most modern, most practical method’.

The research report included recommendations to improve the calculations. According to Hordijk, improvements have been made. The research chair is convinced that measuring more does not lead to a different result. “The global pattern will not change.”

Watch this explanatory video on nitrogen calculations from the University of the Netherlands:

Leave a Comment