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Institute of

WO Forest Ecosystems

Healthy air, healthy planet: 2nd International Day of Clean Air for Blue Skies

With the International Day of Clean Air for Blue Skies on 7 September, the United Nations issues for the second time a global call for action toward a single, unifying objective: clean air for all.

© United Nations Environment Programme
© United Nations Environment Programme

The Thünen Institute supports this cause through national and international forest ecosystem monitoring within the framework of ICP Forests under the UNECE Air Convention. This year, the focus is on the need for healthy air for all, while incorporating other critical issues such as climate change, human and planetary health, and the Sustainable Development Goals into the discussion.

Air pollution is a global problem and poses one of the greatest environmental risks to human health, ecosystem function, and historic and cultural monuments. Although air pollution in Europe has already been significantly reduced in recent decades through various air pollution abatement measures in industry and traffic, it remains at high levels, as evidenced by results of the international forest ecosystem monitoring under ICP Forests.


The International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) of the United Nations Economic Commission for Europe (UNECE) is co-ordinated by the Thünen Institute of Forest Ecosystems in Eberswalde, Germany. Since 1985, scientists throughout Europe and beyond have been monitoring the impact of air pollution and other stressors on forest condition. They are thus able to trace important developments in forest ecosystems such as changes in the nutritional status of trees or in biodiversity over a period of now 35 years.

In addition to the impact of extreme weather and climatic changes, the focus is particularly on ground-level ozone and airborne nitrogen and sulfur compounds. For example, the observed sulfate content in precipitation water in European forests decreased dramatically since the beginning of air pollution control measures in the 1980s (ICP Forests 2020 Technical Report). For nitrogen compounds, the decline has been less pronounced and the level of nitrogen input is still considered critical (ICP Forests Brief No 2).

With up to 7,500 study plots on a 16 by 16 kilometer grid (Level I), the condition of forest trees and forest soils as well as foliar chemistry are studied in Europe and the UNECE region, respectively. On more than 600 selected plots (Level II), additional data are collected on weather and climate, air quality, deposition of pollutants in forests, soil water quality and tree growth, among others.

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