The National Institute for Public Health and the Environment (RIVM) has found a partial explanation for the difference between measurements and calculations of ammonia concentrations along the coast. This has been used to implement improvements in the Operational Priority Substances (OPS) model. The report that has now been published summarises the results. This concludes RIVM’s study into ammonia from the sea. In the National Nitrogen Knowledge Programme (NKS), RIVM has teamed up with other research organisations to study how the model calculations can be further improved.
There is a greater difference between the calculated and measured concentrations of ammonia in the air along the Dutch coast than in other parts of the Netherlands. RIVM assumed that the difference could be explained by the emission of ammonia from the sea. However, this emission of ammonia was overestimated, which is why RIVM has conducted further research.
Better understanding of the difference
Interim reports from 2023 and 2024 showed that the measurements along the coast are correct and that no other ammonia sources can explain (in Dutch) the difference. The reports did show that input data, such as weather conditions, used by the OPS model could be improved in some areas. These data have now been adjusted in the model (in Dutch).The effects of the changes will become visible in the products delivered by RIVM later this year, such as the large-scale concentration maps for the Netherlands (GCN) report and the monitoring report ‘Nitrogen deposition in Natura 2000 areas’.
The changes have reduced the difference between measurements and calculations along the coast by 20%. The calculations made there now deviate from the measurements by around 40%. On average, this is 30% in other parts of the Netherlands.
Further research into improving models
Every scientific model has its uncertainties. To determine the extent to which uncertainties in the OPS model contribute to the difference along the coast, RIVM and TNO compared the OPS model with two other models. This revealed that all models calculate the concentrations along the coast lower than showed by the measurements, suggesting that the differences in all models have the same cause. One possible cause is that it is not yet entirely clear how the emission of ammonia varies in different parts of the Netherlands and over the year.
RIVM, along with its NKS partners, is looking into ways to improve the mapping of the emission of ammonia and nitrogen oxides. RIVM expects that the results will help explain a larger proportion of the concentration of ammonia along the coast. Together with the province of South Holland and drinking water company Dunea, RIVM is also launching an extensive campaign to measure nitrogen deposition in the Solleveld dunes this year. These measurements may offer suggestions for further improving deposition calculations in said dunes.