Air Knows No Borders: The State of Transnational Air Quality Agreements
By Francesca Mills, Yale Conservation Scholar at OpenAQ
Whether it’s wildfire smoke drifting across continents or urban smog seeping into neighboring countries, air pollution does not respect borders. For example, in June 2023, images of New York City’s sky turning orange due to Canadian wildfire smoke made news. Countries in the Indo-Gangetic Plains are significantly impacted by regional transport. Dust from the Sahara Desert pollutes neighboring countries and continents and can even travel over the Atlantic. But while pollution travels freely, regulations do not. For example, in Japan and Korea, local particulate matter pollution, where respective national laws apply, only contributes up to 30% — the rest comes from transboundary air pollution [1].
Air pollution is therefore a global challenge that transcends political borders, requiring coordinated responses from nations and regions. To address this shared threat, a growing number of international agreements and regulatory frameworks have been established to regulate air quality, reduce harmful emissions, and protect human and environmental health [2]. Multilateral, transnational agreements can mitigate the health and ecological impacts of air pollution that crosses national borders, while national regulations are confined to within that nation’s borders. This blog examines existing transnational air quality standard-setting agreements, their operational frameworks, and the challenges and opportunities associated with implementing them.
What Are Air Quality Standards?
Air quality standards are legally defined limits on the concentration of harmful pollutants in the air, designed to protect both public health and the environment. These limits apply to key pollutants, including fine particulate matter (PM2.5), ground-level ozone (O₃), nitrogen dioxide (NO₂), carbon monoxide (CO), sulfur dioxide (SO₂), and lead [3].
Because the distribution of air quality does not align neatly with national boundaries, global action is needed to align standards, reduce harmful emissions, and protect the worldwide community from the serious health and environmental impacts of polluted air. Examples of agreements that carry out transnational standards include the EU’s Directive 2024/2881 on Ambient Air Quality and Cleaner Air for Europe, the Convention on Long-Range Transboundary Air Pollution (LRTAP), the Association of Southeast Asian Nations (ASEAN) Agreement on Transboundary Haze Pollution in the Southeast Asia region, and the U.S.-Canada Air Quality Agreement.
Four Examples of Transnational Air Quality Agreements
EU’s Directive 2024/2881 on Ambient Air Quality and Cleaner Air for Europe. The European Union (EU) operates under a complex system of laws that aim to harmonize policies across its member states. These laws encompass a broad range of areas, including environmental protection, consumer rights, and trade regulations. The European Union (EU) maintains some of the world’s most comprehensive air quality standards, designed to protect human health and the environment. The Commission can identify potential violations of EU law through its investigations or in response to complaints from citizens, businesses, or other stakeholders. These standards, outlined in the Ambient Air Quality Directive (2008/50/EC), set legally binding limits for major air pollutants such as PM10 and PM2.5, NO₂, O₃, SO₂, CO, and lead [4].
As part of its ongoing environmental initiatives, the EU has proposed new air quality targets for 2030 that align more closely with the World Health Organization’s (WHO) recommendations. These goals are accompanied by a regular review cycle, beginning in 2028 and recurring every five years, to ensure the standards remain current with the latest scientific advancements and responsive to emerging pollutants. Member states are required to monitor air quality, report data to the European Environment Agency, and take corrective actions if limits are exceeded, making air pollution control a shared responsibility across Europe [5]. NGOs and citizens can initiate potential legal actions to compel authorities to comply with air quality standards when violations occur, using rights granted by the Aarhus Convention. Such actions have proven effective, as seen, for example, in Germany, where court rulings mandated municipalities to implement clean air plans, leading to lawsuits that push for better enforcement of EU air pollution laws [6].
Multilateral Long-Range Transboundary Air Pollution Agreement. The 1979 Convention on Long-Range Transboundary Air Pollution (LRTAP) was the first multilateral agreement to address air pollution across national borders, establishing a regional framework for cooperation. Signed in 1979, the LRTAP Convention marked a pioneering step in the development of cross-border air pollution policy. With participation from over 50 countries across Europe, North America, and beyond, the agreement introduced a series of protocols targeting specific pollutants like sulfur and heavy metals [7, 8]. Protocols included:
- Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-level Ozone (1999), which set national emission ceilings for SO2, NOx, VOCs, and ammonia, and established stringent limit values for emissions from specific sources;
- Protocol on Heavy Metals (1998), which addressed lead, cadmium, and mercury;
- Aarhus Protocol on Persistent Organic Pollutants (POPs) (1998), which targets 16 substances and aims to eliminate all discharges, emissions, and losses of POPs by banning specific substances and requiring emissions reduction of certain classes of compounds.
In 2012, amendments were adopted to strengthen the first two protocols, adding black carbon to emission targets and allowing more flexibility in implementation while maintaining effectiveness.
Another key part of LRTAP is data sharing. By standardizing how data is collected and reported, LRTAP enables the coordinated assessment of transboundary pollution and enhances regional capacity to respond effectively to environmental and public health risks. Under LRTAP, parties are expected to engage in coordinated air quality monitoring and data sharing, particularly through the European Monitoring and Evaluation Programme (EMEP). While not all requirements are explicitly mandatory, ratifying specific protocols obligates countries to monitor emissions, track pollutant levels, and contribute to regional assessments of transboundary pollution [9].
ASEAN Agreement on Transboundary Haze Pollution. The ASEAN Agreement on Transboundary Haze Pollution, signed in 2002, was established in response to the significant environmental crisis caused by widespread land and forest fires in Southeast Asia during the late 1990s, especially between 1997 and 1998. It is an environmental agreement among ten ASEAN member states, signed in 2002, aimed at addressing the recurring problem of transboundary pollution. The agreement relies mainly on cooperation, dialogue, and capacity-building to address violations. Countries commit to preventing and monitoring haze pollution, sharing information and resources, and strengthening regional cooperation and early warning systems. Despite the agreement, enforcement remains weak due to limited compliance mechanisms and challenges in striking a balance between national sovereignty and regional action [10]. The Agreement has had limited success due to five key reasons: lack of a regional monitoring and coordination center, bilateral tensions hindering cooperation, weak national legislation and enforcement, conflicting stakeholder interests, and ASEAN’s consensus-based governance model that discourages decisive regional intervention [11].
U.S.-Canada Air Quality Agreement (AQA). Established in 1991, the agreement aims to reduce transboundary air pollution, with a particular focus on acid rain-causing pollutants such as sulfur dioxide SO₂ and NOₓ [12]. Later, amendments were made to include provisions to minimize precursors such as NOₓ and volatile organic compounds (VOCs) and O₃, a component of smog [13]. The AQA complements the Clean Air Act (U.S.) and the Air Quality Management System (Canada). Commitments include coordinated emissions reductions, scientific and technical cooperation, and annual reporting on progress in each country. Under Article V of the Canada-U.S. Air Quality Agreement (AQA), each party is required to notify the other of any proposed actions, activities, or projects that could reasonably be expected to cause significant transboundary air pollution. It also promotes public access to emissions and monitoring databases, encourages consultation and sharing of data, tools, and methods, and supports joint analyses to track health and environmental impacts, inform regulatory policy, and evaluate transboundary pollution transport [14]. Currently, this notification requirement is being applied only to actions occurring within 100 kilometers of the Canada-U.S. border [15]. The agreement has led to significant declines in SO2 emissions, and thus a decline in acid rain and improved air quality in both countries, serving as a successful model for bilateral environmental cooperation [16].
Barriers
Gaps in air quality monitoring and data transparency significantly hinder efforts to understand and address cross-border pollution. In many regions, particularly in low- and middle-income countries, limited access to monitoring infrastructure results in pollution levels being unmeasured or underreported. Without reliable and openly accessible data, it becomes difficult to trace the movement of pollutants across national boundaries, assess their health and environmental impacts, or enforce international agreements. These data gaps also weaken public trust and make it challenging for civil society, researchers, and policymakers to hold polluting countries or industries accountable for transboundary emissions. Strengthening air quality monitoring systems and promoting data sharing are essential steps toward regional cooperation and effective environmental governance.
Challenges
Developing a cohesive transnational air quality plan faces several challenges. Differences in political will and national sovereignty can make collaboration challenging, as some governments may prioritize economic growth over environmental protection or resist external influence on their domestic policies. Second, economic inequality and uneven levels of industrialization mean that countries bear different pollution burdens and capacities to address them, complicating the creation of fair and practical standards. Finally, weak enforcement mechanisms and a lack of accountability reduce the effectiveness of agreements, especially when there are no binding legal consequences for noncompliance.
Summary
While international agreements, such as the EU Air Quality Directive, LRTAP, and the U.S.-Canada Air Quality Agreement, offer promising frameworks, they also highlight the gaps in enforcement, equity, and political will that remain. Stronger monitoring, transparent data sharing, equitable policies, and legally binding commitments must form the backbone of future agreements.
References
[1] Yim, S. H. L., Gu, Y., Shapiro, M. A., and Stephens, B.: Air quality and acid deposition impacts of local emissions and transboundary air pollution in Japan and South Korea, Atmos. Chem. Phys., 19, 13309–13323, https://doi.org/10.5194/acp-19-13309-2019, 2019.
[2] Cotterrell, R., Law’s Community: Legal Ideas in Sociological Perspective. Available at: https://www.law.uh.edu/assignments/spring2014/24345/cotterrell2012.pdf, 2012.
[3] Georgia Environmental Protection Division, National Ambient Air Quality Standards (NAAQS), https://epd.georgia.gov/air-protection-branch/air-branch-programs/planning-and-support-program/national-ambient-air-quality
[4] European Union, Directive 2008/50/EC on Ambient Air Quality and Cleaner Air for Europe, Official Journal of the European Union, https://eur-lex.europa.eu/eli/dir/2008/50/oj/eng
[5] European Commission, EU Air Quality Standards, https://environment.ec.europa.eu/topics/air/air-quality/eu-air-quality-standards_en.
[6] European Commission, Legal Actions on Clean Air — LIFE Integrated Project (LIFE15 GIE/DE/000795), https://webgate.ec.europa.eu/life/publicWebsite/project/LIFE15-GIE-DE-000795/legal-actions-on-clean
[7] U.S. Department of State, Convention on Long-Range Transboundary Air Pollution, https://www.state.gov/key-topics-office-of-environmental-quality-and-transboundary-issues/convention-on-long-range-transboundary-air-pollution/
[8] World Population Review, Eastern Bloc Countries 2024, https://worldpopulationreview.com/country-rankings/eastern-bloc-countries
[9] Association of Southeast Asian Nations (ASEAN), ASEAN Agreement on Transboundary Haze Pollution, 2002. Available at: https://asean.org/wp-content/uploads/2021/01/ASEANAgreementonTransboundaryHazePollution-1.pdf.
[10] Association of Southeast Asian Nations (ASEAN), ASEAN Agreement on Transboundary Haze Pollution, 2002 https://asean.org/wp-content/uploads/2021/01/ASEANAgreementonTransboundaryHazePollution-1.pdf.
[11] Aalde, Alfons, et al. “International Cooperation on Air Pollution: From the CLRTAP to a Global Agreement.” Environmental Law Review, vol. 24, no. 4, 2022, pp. 305–317. Available at: https://ui.adsabs.harvard.edu/abs/2022EnvLR..24..305A/abstract.
[12] Canada-United States Air Quality Agreement: overview. https://www.canada.ca/en/environment-climate-change/services/air-pollution/issues/transboundary/canada-united-states-air-quality-agreement-overview.html
[13] Amending The “Agreement between the government of Canada and the government of the United Sates of America on Air Quality.” https://www.canada.ca/en/environment-climate-change/services/air-pollution/publications/canada-united-states-quality-agreement-ozone-annex.html
[14] Agreement between the Government of Canada and the Government of the United States on Air Quality (AQA). https://www.canada.ca/en/environment-climate-change/corporate/international-affairs/partnerships-countries-regions/north-america/canada-united-states-air-quality.html
[15] Government of Canada, Canada–United States Air Quality Agreement: Notifications, https://www.canada.ca/en/environment-climate-change/services/air-pollution/issues/transboundary/canada-united-states-air-quality-agreement/notifications/form.html.
[16] U.S. Environmental Protection Agency, U.S.-Canada Air Quality Agreement, https://www.epa.gov/international-cooperation/us-canada-air-quality-agreement.
