Atmospheric Deposition of Nitrogen to the OSPAR Maritime Area in the period 1995-2018
Nitrogen deposition to the OSPAR Maritime Area for the 24-year period 1995-2018 has been calculated with the EMEP MSC-W Chemistry Transport Model on a horizontal resolution of 0.1 x 0.1 degrees.
Data on annual deposition of nitrogen are provided in this report for each of the 5 OSPAR Regions and the 24 Extended Economic Zones (EEZs), for each year within the trend period 1995-2018. As usual, depositions of nitrogen are calculated separately for oxidised nitrogen (NO, NO2, etc.) and reduced nitrogen (ammonia, ammonium nitrate, etc.) as these two groups of nitrogen-containing molecules have different emission sources and thus require different policy measures for mitigation.
According to our model results, annual deposition of oxidised nitrogen was clearly lower in 2018 than in 1995 in all OSPAR Regions, with the largest decline in Region V (52.2%). Annual deposition of reduced nitrogen decreased in three out of five OSPAR Regions, but the reductions are much smaller than in the case of oxidised nitrogen. Increases are calculated for OSPAR Regions II and IV. Concerning annual deposition of total (oxidised+reduced) nitrogen, there is a decline between 1995 and 2018 in all Regions (in the range 20.4-41.4%), the largest decline being in Region V.
In all considered EEZs, there is a clear decline in the annual deposition of oxidised nitrogen between 1995 and 2018 (in the range 18.1-57.8%), while the annual deposition of reduced nitrogen was higher in 2018 than in 1995 in 18 EEZs. In 6 EEZs, deposition of reduced nitrogen has decreased as well, by up to 25%. In all considered EEZs, the annual deposition of total nitrogen has decreased from 1995 to 2018 (in the range 3.4-48.4%).
It has to be noted, however, that percentage changes reported here with respect to the reference year 1995 can vary significantly from year to year due to meteorological conditions. This is especially true for the smallest EEZs. Therefore, we have calculated changes in 5-year means as well, allowing for more robust results.
This year, changes with respect to earlier reports have also occurred due to a change in area definitions of OSPAR Regions II and III.