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Atmospheric Deposition of Nitrogen to the OSPAR Maritime Area in the period 1990-2020

Executive Summary

Airborne nitrogen depositions to the OSPAR Maritime Area for the 31-year period 1990-2020 have been calculated with the EMEP MSC-W Chemistry Transport Model on a horizontal resolution of 0.1°longitude x 0.1°latitude, based on emission data updated in 2022 by the EMEP Centre on Emission Inventories and Projections. The 1990-2020 period is the longest period for which EMEP MSC-W has done this type of calculation for OSPAR until now.

Results for actual and weather-normalized nitrogen depositions are presented in this report and accompanying data sheets for the 5 OSPAR Regions, the 24 Exclusive Economic Zones (EEZs) within the OSPAR Maritime Area, the 25 so-called ‘partial EEZs’ (EEZs divided up into different OSPAR regions), and the 64 COMP4 (Fourth Common Procedure) Assessment Units. The new definitions of the COMP4 Assessment Units (as of August 2022) were implemented in the EMEP MSC-W analysis routines as part of this contract. Normalization (“weather-averaging”) was done using meteorological data for the years 2016 to 2020.

According to our model results, actual (non-normalized) depositions of oxidised nitrogen were clearly lower in 2020 than in 1990 in all OSPAR Regions, EEZs and COMP4 Assessment Units. In the case of reduced nitrogen depositions, there are both increases and decreases, depending on the receptor area under consideration. This is mainly due to the much less significant (or even absent) downward trends seen in the emissions of reduced nitrogen in many countries. However, total (oxidized+reduced) nitrogen depositions were lower in 2020 than in 1990 in all OSPAR Regions, all EEZs and nearly all COMP4 Assessment Units.

This year, we have included a trend analysis for depositions over the 31-year period from 1990 to 2020, but also separately for the 1990s and for the most recent decade (2010-2020), using the Mann-Kendall test. Statistically significant downward trends are found in all receptor areas for oxidized nitrogen, while for reduced nitrogen there are far less areas with significant downward trends; indeed some of them show increases. In general, trends in weather-normalized depositions are more significant than those in actual depositions because the interannual variability in meteorology is filtered out.

Full Report

Nitrogen emissions 2020 data

Nitrogen depositions 2020 data