The legacy of the Nordic contributions to acid rain science and policy.

The legacy of the Nordic contributions to acid rain science and policy - PMC Skip to main content An official website of the United States government Here's how you know Here's how you know Search Log in Primary site navigation Search Log in Search PMC Full-Text Archive Search in PMC Journal List User Guide As a library, NLM provides access to scientific literature. Inclusion in an NLM database does not imply endorsement of, or agreement with, the contents by NLM or the National Institutes of Health. Learn more: PMC Disclaimer | PMC Copyright Notice Ambio . 2025 Dec 7;55(7):1531–1543. doi: 10.1007/s13280-025-02304-8 The legacy of the Nordic contributions to acid rain science and policy Øystein Hov 1 , Peringe Grennfelt 2, ✉ Author information Article notes Copyright and License information 1 Norwegian Meteorological Institute, Henrik Mohns Plass 1, Blindern, P.O. Box 43, 0313 Oslo, Norway 2 IVL Swedish Environmental Research Institute, Aschebergsgatan 44, P.O. Box 53021, 40014 Gothenburg, Sweden ✉ Corresponding author. Received 2025 Mar 11; Revised 2025 Aug 22; Accepted 2025 Oct 30; Issue date 2026 Jul. © The Author(s) 2025 Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/ . PMC Copyright notice PMCID: PMC13230451  PMID: 41353674 Abstract For more than 50 years, the Nordic countries have together played a significant role in Europe in raising awareness, scientific understanding and policy development for the control of acid rain and related air pollution problems. The Nordic cooperation has most of the time been organised by the Nordic Council of Ministers. It began within OECD in 1969 and was followed by the establishment of the European Monitoring and Evaluation Programme (EMEP) under UNECE and the Convention for Long-Range Transport of Air Pollutants (the Air Convention), signed in 1979. This paper examines Nordic collaboration across three distinct phases: 1970–1980, 1985–2000 and post-2000. We analyse the defining characteristics of each period and their varying influences on international policy development in Europe, initially focusing on the Air Convention and later extending to the European Union. Finally, we explore potential pathways for maintaining an influential international role of the Nordic countries in advancing air pollution control when climate change, energy transition, increased security uncertainties and the AI revolution pose significant challenges and opportunities for air pollution management and control. Supplementary Information The online version contains supplementary material available at 10.1007/s13280-025-02304-8. Keywords: Acid rain, Air pollution strategies, CLRTAP, EU, Nordic collaboration, Science diplomacy Introduction Beginning in the late 1960s, the understanding of air pollution in Europe underwent a significant transformation. Observations from Nordic countries 1 revealed that air pollution was influenced by distant sources often in other countries. A notable concern was the widespread fish mortality in lakes and streams, which was linked to acid precipitation caused by the long-range transport of airborne sulphur across Europe (Odén, 1967 , 1968 ). This problem required international attention. The scientific, technical and political activities that followed defined a new international science–policy landscape for addressing air pollution. Research and policy agendas were developed, often with the Nordic countries in complex leading roles and with outcomes that were favourable to them (Sokolovsky 2004 ; Björkbom 2004 ; Rothschild 2015 ). A key result was the Convention on Long-Range Transboundary Air Pollution (CLRTAP, hereafter denoted the Air Convention) under United Nations Economic Commission for Europe (UNECE). This ground-breaking environmental agreement was signed in 1979 by 34 European countries, Canada, the USA and the European Economic Community (EEC, now the European Union, EU). The early focus on sulphur dioxide emissions and acid rain later expanded to include photooxidants, reactive nitrogen compounds, persistent organic compounds, mercury and other heavy metals due to their adverse effects on human health, food production, forestry and ecosystems (Grennfelt et al. 2020 ). The Air Convention became a pioneering instrument for protecting environment and public health by reducing emissions, where scientists across many disciplines over time have provided a robust foundation for policymakers to negotiate emission reduction commitments (Dovland et al. 2004 ). The Air Convention has fostered extensive scientific, technological and political cooperation, setting an example for other regions and globally as well as for other environmental threats. In this paper, we examine and discuss how the Nordic countries together from the very beginning took a leading role in the formation of acid rain science and policy. We describe the lessons learned from more than 50 years of successful international cooperation to understand and control transboundary air pollution and their implications for future environmental control developments. We highlight prerequisites and initiatives that have made the Nordic role and influence successful. We analyse three different phases of Nordic collaboration in developing science-based regional environmental policies since the late 1960s: Late 1960s–1979: A Nordic science–policy network on air pollution was established leading to organised systems for monitoring and assessment within the Nordic countries and on a pan-European scale (EMEP) and finally for international policy (the Air Convention). 1985–1999: Nordic initiatives helped form a systematic approach for science–policy interaction, which included development of the critical loads concept and cost-effective, effect-based emission reduction agreements with the Gothenburg Protocol (GP) under the Air Convention and the EU National Emissions Ceilings Directive (NECD) as the most important outcomes. 2000–2020: Nordic initiatives to foster international collaboration on air pollution in a broadening environmental and societal context, including climate change, human health, food security and the distribution of air pollution globally. In the concluding chapter, we discuss how Nordic leadership could and should be more effectively leveraged in addressing global challenges, including climate change, human health, biodiversity loss and other environmental stresses encapsulated in the UN Sustainable Development Goals. 2 We argue for stronger Nordic collaboration informed by the acid rain legacy with its strong collaborative culture and science elements and supported by available and emerging technologies including the observation and modelling of biogeochemical cycles to analyse environmental threats and their mitigation. The discussion is limited to the parts where Nordic involvement was important for science and policy development. Initiatives and efforts by other countries and organisations were increasingly important from the 1990s and onwards, but we do not focus on these. The preparation of this paper has included collecting and researching of extensive material not published previously. Summaries and additional details can be found in the Supplementary Information , which is organised in parallel with the chapters below. The building of science and policy platforms, late 1960s–1979 Several elements acted together in the late 1960s and 1970s in building the Nordic science and policy platforms for the understanding of acid rain, its causes and how it was communicated to become an environmental issue on a European scale. Public awareness Svante Odén’s article in Dagens Nyheter in October 1967 (Odén 1967 ) caused immediate public concern in Sweden and Norway, where acid rain became a widely recognised and debated issue (see for example Lundgren 1998 ). The public concern became a crucial factor in establishing a platform for science and policy engagement and action. A socially conscious academic research base The early research interest in biogeochemistry in Swedish academia, beginning around 1950, had developed a scientific thinking that was useful in acid rain research and understanding. Measurements of precipitation chemistry started at the end of the 1940s and included studies of the deposition of reactive nitrogen over Sweden (Ångström & Högberg 1952 ). The results showed that deposition was significant for the nutrient supply to soils (Bolin 1999 ). Based on these observations, the European Atmospheric Chemistry Network (EACN) was initiated, a precursor to the acid rain observation network that started later. An important milestone was Sweden’s case study for the first United Nations Conference on the Human Environment held in Stockholm in 1972 (Bolin et al. 1971 ). That study, together with the growing interest in atmospheric deposition arising from the EACN observations, was a basis for the alignment that took place between academia and societal needs, establishing a “Science for Society” ethos. The mutual engagement between researchers and policymakers fostered a culture of trust and collaboration, advancing both societal risk reduction and academic innovation (Lidskog & Sundqvist 2011 ). A Nordic environmental research sector alongside academia and policymakers in government From the late 1960s, environmental research institutions were set up in the Nordic countries outside the university sector in the wake of growing environmental movements, as were government environmental ministries and agencies. 3 These new institutions fostered a cadre of experts within research frameworks designed to support the development of national and international pollution abatement policies. Acid rain became a model for how exploratory research and informed policy development could successfully act together. Bringing research, policy and collaboration into action Sweden and Norway put pressure on the European OECD countries to investigate the acid rain problem. Following a meeting of the OECD Air Management Sector Group in 1969 (OECD 1969 ), the Nordic countries offered to establish a group of experts from their countries to plan a scientific investigation, and in July 1972, the “OECD project” began, coordinated by NILU and partly funded by Nordforsk, an organisation that fostered Nordic cooperation. The project, which mainly was set up by the Nordic research institutions mentioned in footnote 3, included two main activities (Ottar 1975 ): Establish a broad European collaborative study of sulphur transport and acid deposition. Initiate a parallel Nordic initiative integrated into the larger European OECD project. The Nordic activities became in this way a pilot for the OECD project. Scientific methods were tested within the Nordic community before they were proposed to the OECD community. The report from the OECD project was put together at NILU with support from Nordforsk, and it clearly demonstrated long-range transport of sulphur across Europe. In fact, the report included the first “blame matrix” calculation of the exchange of sulphur between the participating countries (OECD 1977 ). The tabulated matrices then became standard output in the annual EMEP reporting and were important for understanding the need and benefit of acting together to reduce impact of the atmospheric deposition. The experience from Nordforsk and OECD formed the scientific basis when EMEP was established in 1977 (EMEP 1984 ) and the Air Convention in 1979. The OECD project and the blame matrix calculations showed that it was important to include East Europe in a pan-European acid deposition observation network. The Nordic countries took a lead. Norway invited the main countries on both sides of the Iron Curtain to a workshop in Oslo in December 1974, and 17 countries and several international organisations took part. The meeting was a breakthrough for a pan-European approach as the Soviet Union supported the meeting through the Council for Mutual Economic Assistance (CMEA), an organisation involving all countries in the East. The Norwegian Minister of Environment Gro Harlem Brundtland opened the meeting by pointing to the importance of science in finding common solutions to air pollution problems. The meeting concluded that a long-term pan-European programme built on the elements and experience from the OECD project should be established, UNECE could be its host and WMO could contribute to the implementation. 4 At the government level, Gro Harlem Brundtland aligned the interests of the USSR and Norway in setting up a treaty to control sulphur dioxide emissions in Europe. She was instrumental in a crucial diplomatic step: the establishment of a level playing field with the USSR. She was invited to the Soviet Union and visited Moscow in early 1978, where it was agreed that the two countries should cooperate and seek a decision on the drafting of the convention (Sokolovsky 2004 ). From a Nordic scientific project to a Nordic intergovernmental body linking science and policy The Nordic leadership in air pollution research in the Nordforsk project (1969–1975) transitioned in 1976 into a formal intergovernmental body, the Air Management Group (AMG), under the Nordic Council of Ministers (NCM). AMG received an annual budget to fund research in support of policy development. This transformation solidified the link between research and environmental policymaking and reinforced the Nordic dimension and legitimacy of the endeavour. Air pollution, persistent organic pollutants and heavy metals were included in the Nordic collaboration. The Nordic governments appointed members to the AMG, in the beginning often the experts already involved in the Nordforsk project. Political externalities in the cold war context The Swedish diplomat Lars Björkbom argued that processes and policies external to the Air Convention were important for its success (Björkbom 2004 ). Security, trade, economics, and cultural and other political factors had, according to him, been underestimated or even disregarded. He provided an important lesson learned when he said that “it is not possible to understand the politics leading to the (Air) Convention by considering environmental policy goals alone. It only makes sense if the elements and logic of the cold war are brought in”. The contribution of the Norwegian minister Gro Harlem Brundtland is an example when she established a level playing field with the USSR in preparation of the Air Convention. Several smaller steps together formed a vital process. The Nordic experience as a science–policy model The thinking behind a complex undertaking like the OECD project and later the plans for EMEP were articulated by Ottar ( 1975 ). The work organised in Nordforsk and OECD was undertaken jointly by Nordic scientists and policymakers and included several scientific disciplines in a systems approach to the problem. A dynamic structure evolved, where learning, exchange of experience, revision of beliefs and recruitment of expertise took place over time, enabling significant progress in air pollution control. The Nordic experience became a model for the development of science–policy collaboration in Europe and formed the basic elements of EMEP and other bodies within the Air Convention. The second phase of the Air Convention 1985–2000 In spring 1983, the Nordic countries proposed a first protocol with the aim to reduce emissions in Europe by 30%. The proposal garnered support from several nations on the European continent such as the Federal Republic of Germany, driven by public concern over forest dieback (Ulrich 1980 ). As an outcome, the first protocol on sulphur was signed in 1985. Nordic countries continued to advocate for further emission reductions. Using the AMG as a collaborative platform, they supported research and workshops to define steps forward, now with the aim to develop strategies that were more science-based. The AMG set up two expert groups, one on Atmospheric Processes (EGAP) and one on Effects (EGE). The expert groups discussed scientific needs, proposed new projects and developed scientific ideas for future agreements. In addition to sulphur, the agenda now expanded to include reactive nitrogen compounds, ozone and volatile organic compounds. The Nordic expert groups In the 1980s, EGAP supported EMEP and the Air Convention in atmospheric modelling and calculation of source–receptor relationships. Blame matrices were developed for oxidised nitrogen, ammonia and finally ozone (Hov et al. 1987 ). The regional formation and long-range transport of ground level ozone had been known since the early 1970s and was incorporated into the Air Convention discussions towards the end of the 1980s. In the mid-1980s, AMG supported the evaluation of European ozone observations, and when kept together with EMEP calculations, it was shown that ozone was transported across national boundaries and was thus a matter that the Air Convention needed to consider (Eliassen et al. 1982 ; Grennfelt et al. 1989 ). The network for ozone monitoring in Europe expanded and became mandatory within EMEP. EGAP led the development of the Critical Loads (CL) concept and introduced it to the Air Convention (Fig. 1 ). EGE took initiatives and supported science workshops in Norway and Sweden (Nilsson 1986 , Nilsson & Grennfelt 1988 ). The first workshop was science centred with largely Nordic experts; the second a science–policy meeting with scientists and policymakers from all of Europe. The recommendations from the second workshop were presented for the Air Convention in the autumn of 1988, and the Executive Body decided that further agreements should be built on the CL-concept. Through this stepwise approach, first a science meeting, then a science–policy one, CL was widely accepted among both scientists and policymakers and became a part of integrated assessment modelling (IAM) at IIASA and used for assessments and for the quantification of emission control measures. AMG supported also Nordic expert involvement in the IAM work at IIASA. Fig. 1. Open in a new tab An early attempt to present critical loads for nitrogen in forest ecosystems (from Nilsson 1986 ). The figure, appearing on the front page of the workshop report, shows that for forest ecosystems, atmospheric deposition below approximately 10 kg N ha −1 yr −1 nitrogen leaching (runoff) is negligible, while for higher deposition substantial leaching may occur System thinking and linking to policy in the air convention To follow air pollutants from source to environmental and economic impacts and provide the link between sources and effects, a system approach was taken. International Co-operative Programmes (ICPs) for the monitoring and study of effects on ecosystems and materials were organised under WGE, several of them were initiated and run by Nordic institutions, sometimes with Nordic support. The IAM calculations of cost-effective reductions of emissions had to be done and explained so that the countries accepted them. To discuss this issue, AMG organised a workshop in 1992 in Norway with science and policy experts from the Nordic countries. Anton Eliassen at the Norwegian Meteorological Institute and MSC-W presented the so-called gap closure concept, which then became a key for the upcoming protocols (Dovland 1992 ), as shown in Fig. 2 . Fig. 2. Open in a new tab Early attempts to demonstrate the gap closure principle used for the 2nd Sulphur Protocol with Anton Eliassen’s hand-drawn proposal (left). The idea was to reduce by a given percentage the gap between the present load and the critical load, which can be sustained by the ecosystems at each site across Europe. The first scheme for the multi-pollutant, multi-effect Gothenburg Protocol was also presented at the same workshop (right), with the links between the various emitted compounds and effects at different receptors (Dovland 1992 ) Also discussed was an integrated assessment approach to the revision of the Convention’s protocol on nitrogen oxides signed in 1988. Hov and Grennfelt (Grennfelt et al. 1994 , Dovland 1992 ) showed that a scientifically sound solution could only be achieved if models were able to consider several pollutants (ammonia, SO 2 , NOx, hydrocarbons, ozone) and effects simultaneously and suggested this to be the way forward for the Air Convention, as shown in Fig. 2 . These two ideas were accepted by the Air Convention. Gap closure was first used in the Second Sulphur Protocol signed in 1994, and the ideas for including all relevant pollutants were integrated in IIASA’s IAM work, which then was central for the Gothenburg Protocol (GP) signed in 1999. 5 Marine issues integrated with AMG In 1993, the Nordic Council of Ministers merged the Air Management Group with its parallel group on marine pollution into the “Sea and Air Group”, still denoted AMG here. The intent was to transfer the experience using integrated models for air pollution policy development, to marine issues and develop a more open science–policy culture for negotiations and agreements within Helcom and Ospar. 6 But after several attempts to integrate activities among the different Nordic marine modelling groups by finding common ground for models, observations, data handling and applications, it was concluded that individual national research and management cultures persisted, and the communities were unprepared for joint development. This was expressed in the conclusions from a workshop in Göteborg 2003. 7 A few years later the Nordic collaboration in the combined Sea and Air Group ended. Through this decision, an important opportunity was lost for the Nordic countries to take a lead in a coupled and unified approach to regional earth system understanding, comprising the atmosphere, the ocean, freshwater as well as biogeochemistry including pollution. Systems for science–policy interaction emerged during the second phase Helpful concepts and scientific understanding were formulated in the Air Convention work, thanks not least to the support from AMG. In AMG, science and policy experts worked together, had a good overview of the activities in the bodies under the Convention and could take initiatives often as an immediate response to a need or request to move policy forward. The situation in the EEC/EU was different. The EEC/EU system took advantage of the Convention experience, but without the close and continuous dialogue between the science support community and the policymakers. Specific research questions were formulated by the European Commission and addressed through a competitive tender process with deadlines and deliverables. Until 1995, Denmark was the only Nordic EEC/EU country. At AMG meetings, a standing item on the agenda was the Danish report on ongoing work within the European Commission, often followed by a discussion of the consequences for the Nordic countries. Denmark also brought back Nordic views to the European Commission. In 1995, Finland and Sweden joined the EU, and the three Nordic EU countries informed the remaining two. Often a common view was formed vis-a-vis the European Commission. Nordic experts had also from the early 1980s direct access to the scientific discussions on air pollution priorities through the concerted action COST61 projects. With the entrance of Finland and Sweden, the Nordic influence in the EU increased. In 1997, EU followed an initiative by Sweden and developed an acid rain strategy (European Commission 1997 ). The 2001 National Emissions Ceilings Directive (2001/81/EC) setting national emission reduction obligations was nearly a copy–paste version of the GP. Based on the model developed in the Nordforsk and OECD projects, the Air Convention established an open data and model policy all the way from emission inventories and observations to effect measures and model results. There was a stepwise development of knowledge and policy options. These factors have been essential for the success of the Air Convention and have influenced the air pollution policy work within the EU, not least seen in the way IAMs are used. During the second phase, many parties to the Convention including the EEC/EU initiated scientific activities in support of the regional air pollution agenda. Some of them were very significant in terms of science community involvement and output, e.g. the Eurotrac program. 8 The significance was often indirect; however, the scientific understanding progressed while the direct contribution to the policy development was more limited. Lessons learned in the second phase Blame matrices, critical loads and gap closure were three concepts that had a constructive impact on the communication between science and policy. They allowed the development of IAMs (see Fig. 3 ) with the purpose to calculate how to meet the environmental goals while sharing the costs in an even-handed way among the countries. Fig. 3. Open in a new tab In the first protocols to the Air Convention, there was a direct relationship between basic science and policy development (upper part). The GP was based on the results of integrated assessment modelling of an optimal distribution of ecosystem improvements across Europe and sharing of the costs (lower part) (based on Grennfelt et al. 2020 ) The terms of reference for the Air Convention were successfully broadened to include the regional components of biogeochemical cycles other than sulphur and of importance for acid deposition and public health: reactive nitrogen, photochemical oxidants and particulate matter. A parallel Nordic effort to encourage a common framework for atmospheric and marine pollution analysis failed as the traditional cultural and institutional barriers were difficult to overcome at the time. AMG was intergovernmental, which expressed the governmental commitment to the science–policy interaction process and enhanced the legitimacy of the Nordic contribution to the development of policies under the Air Convention. The third phase—broadening the scope of international air pollution science and policy Saltsjöbaden workshops By the turn of the century, interest in international air pollution policies expanded to include health effects, climate change and local, intercontinental and global geographical scales. AMG continued influencing the broader agenda by taking initiatives based on Nordic capabilities. The first opportunity to influence the air pollution agenda arose a few months after the GP was signed in December 1999. In Sweden, a new scientific research programme had just started—the ASTA research program 9 funded by the Mistra Foundation to undertake research in support of post-GP policies. As an early activity, the programme and AMG organised a workshop with over 100 scientists, experts and policymakers at Saltsjöbaden near Stockholm in April 2000, to define future needs for science in support of international air pollution policies (Grennfelt et al. 2000 ). Most of the recommendations from the meeting were later incorporated into the work plans of the Air Convention and its subgroups and the European Commission. The success of the first workshop led to a series of six additional so-called Saltsjöbaden workshops held in Göteborg, the latest in 2023. The workshops have formed a basis for new initiatives within the international air pollution community, as shown in Table 1 . AMG supported and was the main organiser of all but one of the seven workshops. Table 1. Saltsjöbaden workshops (the reports from the workshops can be found at https://www.ivl.se/projektwebbar/saltsjobaden-air-science-and-policy-workshops.html ). Between 120 and 220 scientists and policymakers attended each workshop. a Eastern Europe, Caucasus and Central Asia (EECCA) No Place and time Key topics and outcome I Saltsjöbaden 2000 Focus on public health impacts. Support to the EU CAFE programme II Göteborg 2004 Hemispheric transport of air pollution—proposal for a Task Force under the Air Convention. Discussion of the progress of the CAFE programme III Göteborg 2007 Emphasis on Short Lived Climate Forcers (SLCF) and reactive nitrogen. Proposal for a Task Force on Nitrogen under the Air Convention. Climate and air pollution were discussed in view of the upcoming EU climate package IV Göteborg 2009 SLCF and linkages between international air pollution and climate policy. The outcome was presented at COP15 in Copenhagen V Göteborg 2013 Implementation of the revised Göteborg Protocol, in particular for the EECCA countries a VI Göteborg 2018 Outreach to organisations and processes outside the Air Convention (WHO, WMO, OECD, UN Environment etc.) VII Göteborg 2023 Air pollution and health in urban areas. Global cooperation between regions Open in a new tab Following the first Saltsjöbaden meeting health impacts of air pollution came into focus after 2000 with the Joint Air Convention-WHO Task Force on the Health Aspects of Air Pollution set up in 1997. Health impacts of air pollution were addressed in the Saltsjöbaden workshops after 2004, particularly in the context of the EU air pollution control strategy (CAFE) (European Commission 2005 ). Both AMG and other Nordic funders supported relevant research such as the Nordic Welfair project 2015–2020 (Åström et al. 2022 ), advancing research in this field. 10 The load of pollutants like sulphur and ozone has important contributions from sources outside of land-based Europe. At the second Saltsjöbaden workshop, it was recommended that the Air Convention should address this. The Executive Body of the Air Convention then established the Task Force on Hemispheric Transport of Air Pollution (HTAP) and included the Arctic, an important region for the Nordic countries. Global aspects of air pollution problems attracted further interest over time, and at the latest two workshops, these problems were discussed in view of decisions taken at UNEP’s first UN Environment Assembly in 2015 and the WHO General Assembly in 2016 to promote action to improve air quality globally. 11 These discussions led to a new Task Force for International Cooperation on Air Pollution as a body under the Air Convention (FICAP). Although air pollution policy shifted from ecosystem impact to health and climate effects, AMG kept the environmental effects on its agenda. The protection of ecosystems was important in the Nordic countries. Acidification was still a problem, and reactive nitrogen increasingly affected biodiversity. While short-term ozone peaks were mitigated, enhanced background concentrations were a threat to human health, ecosystems and climate. Several AMG projects addressed the effects, with priority on acidification recovery, nitrogen/biodiversity, ozone exposure and the close link between ecosystem effects of nitrogen fertilising and food production. The third Saltsjöbaden workshop led to the formation of the Air Convention Task Force on Reactive Nitrogen (TFRN), which is important for the science underpinning of reactive nitrogen policies. Emissions in Central and Western Europe have declined as the protocols under the Air Convention progressed. Countries in the former Soviet Union (EECCA) have been behind in signing and ratifying the Air Convention protocols. Substantial emission reductions or improvements in air quality have not been realised. Several Saltsjöbaden workshops provided opportunities for experts from these countries to discuss how to speed up air pollution control. Some characteristics of the third phase The Saltsjöbaden workshops allowed AMG to keep a central position for the European air pollution agenda. The outcomes of the workshops helped setting priorities for AMG’s work within the Nordic countries. The broadening of the European air pollution problems to include the EECCA region as well as the recent global initiative of FICAP reflect that AMG has the success of the Air Convention as a high priority. Around 2010, the Nordic science–policy groups on air pollution and climate change, respectively, merged into one group, still denoted AMG here. Since 2000, climate change has overshadowed other environmental issues including air pollution. Public awareness, governmental and non-governmental actors, research focus and funding streams of central importance for air pollution and other environmental issues up to 2000 have all until recently turned to climate change. This is the case in most countries globally. A generation of experts in research and policy making in the environmental sector is now occupied by climate change, its mitigation and adaptation, often making other international environmental problems less visible. AMG has, however, kept its priority on air pollution issues and integrated the climate aspects when relevant. Lessons learned The acid rain science to policy process from a knowledge theory perspective The science–policy interaction was essential in the establishment and operation of the Air Convention, first on the Nordic level and then in Europe. The science experts interacted with the policymakers over time to provide science knowledge to the policy issues, and policy issues could redirect or trigger new research (Pielke 2007 ; Grennfelt et al. 2020 ). Science assessments have also been an integral part of the Air Convention, described as an element in science diplomacy (Turekian et al. 2018 ). The approach in Nordforsk and OECD (Ottar 1975 ) compares well with the knowledge theory presented by Donald A Schön in “The Reflective Practitioner” (Schön, 1983 ) as elaborated by Molander ( 1993 ): Knowledge evolves when practised. At the outset the problems to be solved appear complex and not well defined or formulated. With the help of researchers, practitioners can transform an uncertain situation with limited clarity into manageable problems (problem setting). The skilled practitioner can simultaneously reflect, experiment and improvise. According to Molander’s interpretation of Schön’s views, professional knowledge exists within a community of practitioners, forming part of a collective knowledge system. In contrast, academia traditionally adheres to a “technical rationality” framework, where problems are assumed to be well defined and solvable through scientific knowledge and technology. Furthermore, learning from practise requires “voluntary abstention from mistrust” and the willingness “to follow a more experienced leader without knowing from the outset what the outcome would be”. This dynamic or culture has been important in the Air Convention and its subsidiary bodies, where researchers and policy makers—practitioners in their own right—have collaborated over time. The knowledge theory perspective of Schön, Pielke and others reflects quite well the interplay that developed between science and policy in the Air Convention. We believe that it needs to be considered when facing environmental problems with societal implications that require policy action. Integration versus fragmentation in environmental research and policy making There are strong links between abating regional air pollution in the Air Convention framework and climate change mitigation and adaptation. Some of these links have been addressed by AMG and at the Saltsjöbaden workshops. But UNFCCC and IPCC have not really benefited from the Air Convention experiences in the policy process or learned from the mechanisms behind the Air Convention’s success. In the UNFCCC policy development, integrated assessment modelling has not been an expert activity parallel to the negotiations. This can have made agreement of practical mitigation solutions more difficult. Organised groups and entities for policy making, for promotion of special interests and for governance have multiplied over the last decades. Based on Saltsjöbaden recommendations, HTAP, CCAC, TFRN and FICAP have emerged. TFRN, HTAP and FICAP have become integrated into the Air Convention and contribute to its progress. In general, as more and more specialised organisations and groups “occupy” a complex issue like air pollution, new boundaries arise. The transactional costs of self-preservation and the establishment of boundaries to others can constrain transparency and ability to master the required totality of scientific information and policy skills. The evolution of scientific knowledge shows that regional and global biogeochemical cycles reflect the interaction between the earth system elements (atmosphere, ocean, ice, freshwater, terrestrial systems, man-made emissions). For policy development, this means that integration is needed rather than fragmentation. On the other hand, the environmental policy landscape is complex with growing barriers to consensus. Like-minded countries need to join forces when regional or global consensus is out of sight. It is an open and increasingly urgent question for AMG and the Air Convention how to engage in such a complex landscape. Essential discussions are overdue of questions like, for example, how to optimise the co-benefits and minimise the trade-offs in the triade climate–energy transition–nature in future development of environmental and climate policy. Air quality issues cut across climate change, human health, agriculture, urban planning, transportation and water management, as demonstrated by the SDGs. The Air Convention, with its air pollution focus, was not set up to tackle this integration. Its relation with energy and transport is often overshadowed by other policies related to climate, urban planning, etc. In the case of reactive nitrogen emissions, however, TFRN has within the Air Convention addressed upstream issues, going beyond the traditional views on emissions and their control. This is an example for the future. Nordic collaboration as a force in future environmental risk reduction How can regional leadership, such as shown by the Nordic countries in the Air Convention, be practised in the future to lower the societal risks of regional and global air pollution? Air pollution requires continued international attention and action. The European experience should in our view be taken onboard and used in wider contexts than at present. Air quality is poor in many regions globally. The social and psychological consequences are often substantial. Economic inequality is exacerbated. It adds to “the triple burden” 12 of poor communities worldwide (poverty, inferior environmental quality and ill health). It is a global necessity to tackle air pollution. The Nordic countries have a recipe, having for long worked together on improving knowledge and supporting measures to reduce air pollution outside the Nordic area, e.g. within EECCA and through the Saltsjöbaden workshops. We suggest that Nordic collaboration takes place within three circles (Fig. 4 ) with: continued focus on “internal” Nordic issues and in a wider geographical context use the SDGs to frame integrated assessments and control develop a systematic Earth System approach for impact and risk assessments Fig. 4. Open in a new tab Specific Nordic air pollution issues, air pollution issues related to the Earth System and air pollution related to the UN Sustainable Development Goals to build a strong scientific base and act on the links to policy in a “science for service” or “science for action” framework. In the SDG circle in Fig. 4 , AMG should strengthen its involvement in the air pollution footprint of societal sectors dealing with energy, climate change mitigation, public health, land use-ecosystems, food and agriculture, and linked to fresh and marine waters. Growing Nordic security concerns may increase the focus on self-reliance in the food/agriculture and energy sectors, which can affect the air pollution situation. Following the Earth System circle, pollution emissions occur in the biogeochemical cycling of carbon, nitrogen, sulphur, halogens, organic substances including persistent organic matter and heavy metals. These cycles operate in the coupled atmosphere, ocean, cryosphere, fresh water and terrestrial system and depend on human activities including land use and fossil fuel consumption. In the Earth System approach, pollution emission changes from modified agricultural practises and other land use, e.g. related to renewable energy production, can be followed with much in common with the analysis of the pathways to the SDGs (see Fig. 4 ). Climate change has significant consequences for terrestrial and marine biogeochemical cycles and their anthropogenic components. As the energy transition is gaining momentum away from fossil fuel use to renewables and electrification of all societal sectors, there will be significant modifications of the biogeochemical cycles of S, N, VOC, C and PM. It can be argued that the current knowledge of the complex dynamics and interdependence of biogeochemical cycles in an Earth System framework (atmosphere, ocean, ice, terrestrial systems, freshwater and man-made emissions) is not sufficiently integrated into international rules and regulations or in the policy work. The Nordic countries could act together and provide pilot examples. Operational services have grown rapidly and provided help to reduce environmental risks in the short and long term. Examples in a Nordic collaborative setting include weather forecasting and forecasting of dispersion of air and marine pollution. A new direction for the Nordic countries acting together could be to demonstrate how experience gained from operational environmental services can inform and support the management of risks related to air, water, ocean and soil pollution. The AI revolution provides additional strength, quality and value to many aspects of earth system modelling. Operational environmental services offer extensive datasets for AI model training and validation (Bodnar et al. 2025 ). In the Nordic countries, research and governance of the earth system compartments traditionally have been disciplinary and national. An exception is weather prediction, which today is done jointly between Norway, Sweden, Finland and Estonia. 13 A blueprint could be attempted for biogeochemical cycles, the hydrological system including pollutants, and marine forecasting and biogeochemistry. It would not be straight forward to achieve this as the culture for science and services is different in hydrology, oceanography and the cryosphere compared to weather prediction and air pollution. Cross disciplinarity and interoperability are growing, however, not least in observations from satellites and marine platforms. 14 We recommend investigating in a Nordic framework how operational regional Earth System analysis skills can enhance capabilities in environmental risk analysis and countermeasures. W ater as a carrier of biogeochemical substances could be a joint theme focusing on the Nordic countries and adjacent seas including the North Atlantic and the Polar Ocean, the atmosphere and runoff to sea. A relevant partner for AMG would be the European Copernicus programme, a substantial, high quality, underexploited European and global resource. 15 In the current political climate, there are strong common grounds for a closer Nordic collaboration in the Arctic because of the rapid environmental and climate changes there and enhanced security concerns. The cycling of biogeochemical substances is heavily impacted by the thawing of permafrost, changes in terrestrial ecosystems, enhanced wildfires and reduced ice cover, which modifies the carbon cycle as well as the other biogeochemical cycles including those caused by air pollution emissions. Significant political externalities have emerged since 2020, complicating traditional scientific cooperation (including data collection and exchange), and long-standing treaties in Europe and elsewhere are under pressure. The consequences need to be addressed, and the Nordic countries are well placed to do so: The ongoing undermining of a rules-based, globalised science (and policy) field and the accompanying risk of a weakening of the exchange of data, information, knowledge and people as well as of international organisations like WMO. Large countries in terms of size, population and economy often dominate in international negotiations. To balance such asymmetries, smaller countries can form alliances as the Nordic countries have done in the negotiations under the Air Convention and UNFCCC. The future development of environmental policy and safety will benefit from a joint, active Nordic role. Supplementary Information Below is the link to the electronic supplementary material. Supplementary file1 (DOCX 469 KB) (468.4KB, pdf) Acknowledgements We gratefully acknowledge decades of discussions and knowledge sharing with friends and colleagues in the Air Convention community. The Nordic Council of Ministers has been an important source of support. We also thank the anonymous reviewers for their valuable comments that helped make the paper more readable. The Norwegian Meteorological Institute and IVL are acknowledged for their support in preparing this paper. Abbreviations AI Artificial Intelligence AMG Air Management Group (under Nordic Council of Ministers) ASTA International and National Abatement Strategies for Transboundary Air Pollution (MISTRA, Sweden) CAFE Clean Air for Europe (EU) CCAC Climate and Clean Air Coalition (UNEP) CLRTAP Convention on Long-RangeTransboundary Air Pollution (UNECE) CMEA Council for Mutual Economic Assistance CL Critical Load (Air Convention) COP Conference of the Parties (UNFCCC) EACN European Atmospheric Chemistry Network EEA European Environment Agency (EU) EEC European Economic Community EECCA Eastern Europe, Caucasus and Central Asia EGAP Expert Group on Atmospheric Processes (under the Nordic air management group AMG) EGE Expert Group on Effects (under the Nordic Air Management Group AMG) EMEP European Monitoring and Evaluation Programme (protocol to the Air Convention) FICAP Forum for International Cooperation on Air Pollution (Air Convention) GOOS Global Ocean Observation System (IOC, UNESCO) GP Göteborg Protocol (Air Convention) HELCOM Baltic Marine Environment Protection Commission HTAP The task force on Hemispheric Transport of Air Pollution (Air Convention) IAM Integrated Assessment Modelling ICP International Co-operative Programme (Air Convention) IIASA International Institute for Applied Systems Analysis at Laxenburg in Austria IOC Intergovernmental Oceanographic Commission (UNESCO) IPCC Intergovernmental Panel on Climate Change (UNFCCC) IVL IVL Swedish Environmental Research Institute MSC-W Meteorological Synthesizing Centre West at Norwegian Meteorological Institute (EMEP) NCM Nordic Council of Ministers NECD National Emissions Ceilings Directive (EU) NILU Norwegian Institute for Air Research OECD The Organisation for Economic Co-operation and Development OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic SDG UN Sustainable Development Goals SLCF Short-lived Climate Forcers TFRN Task Force on Reactive Nitrogen (Air Convention) UNECE United Nations Economic Commission for Europe UNEP United Nations Environment Programme UNFCCC United Nations Framework Convention for Climate Change WGE Working Group on Effects (Air Convention) WHO World Health Organization WMO World Meteorological Organization Biographies Øystein Hov is a former Director of Research at the Norwegian Meteorological Institute, now part time adviser. His research interests include atmospheric chemistry, earth system modelling, science advice for policy. Peringe Grennfelt is a former Scientific Director at the Swedish Environmental Research Institute IVL. His main scientific activities include atmospheric chemistry, transboundary air pollution and environmental science – policy interactions. Footnotes 1 Denmark, Finland, Iceland, Norway and Sweden. 2 https://sdgs.un.org/goals . 3 The involved research institutions, often formed in the 1960s, included i.a. Norwegian Institute for Air Research NILU (1969), Swedish Environmental Research Institute IVL (1966), The National Laboratory at Risø in Denmark (1955), the Ministry of Environment, Norway (1972), the Swedish Environmental Protection Agency (1967). 4 Cooperative programme for the monitoring and evaluation of the transmission of air pollutants in Europe. Agreed Report Meeting in Oslo 3–5 December 1974. 5 https://unece.org/environment-policy/air/protocol-abate-acidification-eutrophication-and-ground-level-ozone . 6 Helcom is the Baltic Marine Environment Protection Commission (helcom.fi), the Ospar Commission (ospar.org) protects the marine environment of the North-East Atlantic. 7 Hov, Ø. and P. Grennfelt (unpublished) summarised “Workshop on marine modelling 26-27 March 2003: The interest and understanding of policy processes are not much developed among the Finnish, Swedish, Danish and Norwegian participants. None of the marine research groups that up to now have been involved in model work had the interest or prerequisites to take on a broader responsibility”. 8 Eurotrac (European Experiment on Transportation and Transformation of Environmentally Relevant Trace Constituents) was two consecutive European scientific research programmes 1988–2003. 9 International and National Abatement Strategies for Transboundary Air Pollution. 10 https://projects.au.dk/nordicwelfair . 11 https://docs.un.org/en/UNEP/EA.6/Res.10 ; https://apps.who.int/gb/ebwha/pdf_files/WHA69/A69_18-en.pdf . 12 https://www.cleanairfund.org/theme/inequality/ (accessed 2nd March 2025). 13 MetCoOp, see e.g. https://www.met.no/en/projects/metcoop (accessed 5 March 2025). 14 For instance, ocean buoys (Argos floats) contribute in the Global Ocean Observation System GOOS (Alvarez Fanjul et al. 2022 ). 15 Copernicus.eu/en. 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