Abstract

The RIVM manages the calculation tool AERIUS, which calculates and monitors deposition of nitrogen in the Netherlands. Government bodies and project organisers use AERIUS Calculator to calculate nitrogen emissions and deposition of nitrogen in Natura 2000 areas. AERIUS Monitor gives government bodies updates and forecasts regarding nitrogen deposition in Natura 2000 areas and nitrogen overload. Calculator and Monitor facilitate policymaking and licensing.

These calculations and monitoring information must be accurate to enable policymakers and authorities to make the right decisions. For this reason, AERIUS is updated every year with the latest insights and up-todate data. As a result, the results and insights obtained from the latest version of Calculator and Monitor may differ from previous versions. The RIVM has conducted this impact assessment to investigate the significance of these adjustments. For this purpose, the assessment displays the main differences between the versions and the effect thereof.

The update is necessary as data on nitrogen emissions regularly changes. For example, the emission factors, which AERIUS Calculator uses to determine how much nitrogen specific projects will emit, must be kept up to date. Furthermore, in compliance with new legislation, Calculator 2021 calculates deposition levels up to a maximum distance of 25 km from the source, meaning it will give different calculations compared to previous versions.

Every year, the RIVM produces new deposition maps and these are now available via AERIUS Monitor. In addition, the boundaries of the nitrogen-sensitive natural areas in the Natura 2000 regions have been updated (known as the habitat map) and therefore the update will change the locations that AERIUS Calculator uses for its calculations (the relevant hexagons). Moreover, this update affects the previously calculated non-overloaded nitrogen-sensitive natural areas.