Kooi, EThorkelsdottir, GMeijer, PStocker, JLefebre, WVigier, ALans, ASKrol, MJacobs, Cvan Pul, AWichink Kruit, R2025-09-192025-09-192025-09-1910.21945/RIVM-2025-0047https://rivm.openrepository.com/handle/10029/655651<p>Every year, RIVM maps the amount of nitrogen in the air (concentration) and in the soil (deposition) in the Netherlands. RIVM uses models and measurements for this task. These models are also used to develop and implement policy. Models reflect the actual situation as closely as possible, but the calculation remains an approximation. The results may therefore deviate from reality. <br><br>In this study, RIVM compares the results of eight models. Knowledge institutes and governments in various countries use these models to calculate the amounts of nitrogen in the air and the amounts deposited to the soil. <br><br>The comparison was carried out for four different sources of nitrogen and three types of land cover. The sources were livestock housing, manure application to grassland, a tall industrial stack, and traffic on a highway. The types of land cover were deciduous forest, grassland, and a varied landscape with vegetation, buildings, and open space. The models were used to calculate the concentrations in the air and the nitrogen depositions at various distances, ranging between 50 metres and 5 kilometres from the source. <br><br>This study shows that the differences between the models are usually greater for depositions than for concentrations. Furthermore, the differences in concentrations are usually greater for ammonia than for nitrogen oxides. The latter does not apply to depositions of these substances. This study also shows that weather conditions can strongly affect the outcomes. The largest differences in model outcomes occur during very stable weather conditions. Further research into these conditions could increase the accuracy of the models. <br><br>This study is part of the Dutch National Nitrogen Knowledge Programme, the objectives of which include making improvements to the models. Supplementary to this study, we will compare the outcomes of these same eight models to the limited available measurement data at short distances from the sources.</p>application/pdfenReport2025-09-19