Review and revision of empirical critical loads of nitrogen for Europe 2022 (FINAL)

The report describes the scientific background and results of the review and revision of the empirical critical loads of nitrogen established for Europe in 2011 under the umbrella of the UNECE Convention on Long-Range Transboundary Air Pollution (LRTAP Convention). In 2020, the CCE launched a project embedded in the framework of the LRTAP Convention to update the empirical critical loads. New relevant information from studies (2010 - summer 2021) on the effects of nitrogen on natural and semi-natural ecosystems was incorporated into the existing European database on empirical critical loads of N (CLempN). In the current review and revision, gradient studies were used for the first time to assess and determine CLempN. CLempN were structured according to the updated European Nature Information System (EUNIS) classification. Consensus on the results was reached in a UNECE Expert Workshop on Empirical Critical Nitrogen Loadings (26-28 October 2021, Bern, Switzerland) organized by the Swiss Federal Office for the Environment (FOEN), the CCE and the B-WARE Research Center. The findings, presented in Table 1 of the Executive Summary, show that in many cases the outer ranges of empirical critical loads have been reduced. The resulting European database for 2021 includes both revised and newly defined ranges of values for CLempN for each EUNIS class. The results of this report are of significant importance for the protection of N-sensitive natural and semi-natural ecosystems across Europe. This knowledge will be used to support European policies to reduce air pollution.