That is the opinion of a committee of scientists who has investigated this under the leadership of econometrist Leen Hordijk.
With the Aerius system of the National Institute for Public Health and the Environment (RIVM), the emission of ammonia and nitrogen oxides and the precipitation of those nitrogen compounds in protected nature reserves can be calculated. The outcome of such calculations determines, for example, whether a farmer may expand his shed and whether Rijkswaterstaat is allowed to widen a motorway.
Hordijk has two problems with the current use of the system. The main problem is that the nitrogen calculations that the government asks for permit applicants must be so detailed that they cannot actually be produced reliably.
Not reliable enough
In Aerius, the nitrogen precipitation must now be calculated for every hexagon of one hectare in size. At such a small level, the outcome is not reliable enough. « This imbalance can be improved so that Aerius is more applicable for licensing, » says Hordijk. The committee recommends switching to calculations for larger areas. This can be done in the short term.
A second point is that emissions from roads use a different underlying model than for all other activities, from agriculture to industry. When a road is constructed, only the nitrogen oxides that descend within 5 kilometers of that road are counted. This artificial limit only applies to traffic calculations.
That is ‘not justifiable’, the committee believes, because nitrogen compounds are carried much further by the wind. This applies to nitrogen oxides (NH3), which are contained in exhaust gases, among other things, and to ammonia (NH3), which rises from animal manure.
Hordijk makes this clear with figures: « Roughly only 30 percent of the ammonia emitted is 20 kilometers from the source. For nitrogen oxides, this is about 10 percent. »
More measuring points
Minister Carola Schouten (Agriculture) instituted the Hordijk Committee after fierce criticism of the nitrogen calculations by farmers and politicians. The criticism focuses on the Aerius system. The overall opinion on the nitrogen measurements and calculations is positive: they are of sufficient scientific quality.
In an earlier report, Hordijk argued for further improvements. For example, more measurement points should be set up and experts recommend that satellite measurements be used.