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Robust scientific evidence supports revision of EU's clean air standards


September 13, 2023

The Health Effects Institute (HEI) recognizes the outcome of today’s vote from the European Parliament on the revision of the Ambient Air Quality Directive (AAQD), which has remained unchanged since 2008. In particular, the proposed new annual limit values of 10 µg/m3 for fine particulate matter (PM2.5) and 20 µg/m3 for nitrogen dioxide (NO2) across the EU by 2030 and the full alignment with the World Health Organization (WHO) Air Quality Guidelines by 2035 will provide important benefits to public health. The proposal is under consideration in the EU council, and final negotiations are expected in the next several months. 

Air pollution is the top environmental risk to health in Europe. Everyone is vulnerable to its impacts, and some are more at risk than others. People’s level of vulnerability is outside of individual control, as it evolves with age, health condition, socio-economic status, as well as where people live, study, or work.

Although much progress has been made and ambient air pollution continues to decline in high-income regions, epidemiological studies have found health effects at levels below current standards. HEI recently completed a comprehensive research initiative to investigate the health effects of long-term exposure to low levels of air pollution in Europe, Canada and the United States. Particular strengths of the studies included the unprecedented large populations (7-69 million people), with national representativeness, state-of-the-art exposure assessment methods, and thorough statistical analyses with novel methods.

All three of HEI’s low-level studies documented positive associations between mortality and exposure to PM2.5 below the current and proposed European Union limit values and the U.S. National Ambient Air Quality Standards. Furthermore, the studies documented linear (U.S.), or supra-linear (Canada and Europe) exposure-response functions between PM2.5 and mortality, with no evidence for a threshold. A supra-linear function indicates a larger relative effect per additional unit of exposure at low pollutant concentrations than at high concentrations. Together, the research, which was subjected to rigorous HEI peer review, provided important evidence of associations between long-term exposures to low levels of air pollution and health effects, suggesting that reducing air pollution below current standards could yield further health benefits.

Based on these and other studies, the WHO released new Air Quality Guidelines in September 2021. They recommended that annual mean concentrations of PM2.5 and NO2 should not exceed 5 and 10 μg/m3, finding that adverse health effects occur above these values. The European Parliament followed the June vote in the Parliament’s leading environment committee, ENVI, to ensure full alignment with WHO Air Quality Guidelines, albeit the timeline was moved from 2030 to 2035. This is more ambitious than what the European Commission proposed in October 2022. 

Of note, findings from the HEI funded ELAPSE (Effects of Low-Level Air Pollution: A Study in Europe) study were used by the European Commission to estimate the influence of the choice of the exposure-response function on mortality in the accompanying impact assessment. The use of ELAPSE resulted in higher attributable mortality estimates, indicating that the current health burden of air pollution may be underestimated in Europe.

The full reports of all three studies, including a wide range of sensitivity analyses conducted by each team and the Commentaries of the HEI Review Panel, can be found at the Health Effects Institute website www.healtheffects.orgReferences are available below.

Contact: Hanna Boogaard,

About HEI
The Health Effects Institute (HEI) is an independent, nonprofit research institute funded jointly by the U.S. Environmental Protection Agency, industry, and foundations to provide credible, high-quality science on air pollution and health for air quality decisions. HEI’s research is selected, overseen, and peer reviewed by leading subject matter experts on environment and health without involvement of HEI’s public or private sponsors.

Brauer M, Brook JR, Christidis T, Chu Y, Crouse DL, Erickson A, et al. 2019. Mortality–Air Pollution Associations in Low-Exposure Environments (MAPLE): Phase 1. Research Report 203. Boston, MA:Health Effects Institute.

Brauer M, Brook JR, Christidis T, Chu Y, Crouse DL, Erickson A, et al. 2022. Mortality–Air Pollution Associations in Low Exposure Environments (MAPLE): Phase 2. Research Report 212. Boston, MA: Health Effects Institute.

Brunekreef B, Strak M, Chen J, Andersen ZJ, Atkinson R, Bauwelinck M, et al. 2021. Mortality and Morbidity Effects of Long-Term Exposure to Low-Level PM2.5, BC, NO2, and O3: An Analysis of European Cohorts in the ELAPSE Project. Research Report 208. Boston, MA: Health Effects Institute.

Dominici F, Schwartz J, Di Q, Braun D, Choirat C. Zanobetti A. 2019. Assessing Adverse Health Effects of Long-Term Exposure to Low Levels of Ambient Air Pollution: Phase 1. Research Report 200. Boston, MA:Health Effects Institute.

Dominici F, Zanobetti A, Schwartz J, Braun D, Sabath B, Wu X. 2022. Assessing Adverse Health Effects of Long-Term Exposure to Low Levels of Ambient Air Pollution: Implementation of Causal Inference Methods. Research Report 211. Boston, MA: Health Effects Institute.

European Commission (EC). Proposal for a Directive of the European Parliament of the Council on Ambient Air Quality and Cleaner Air for Europe. COM/2022/542 final.

European Commission (EC) Staff Working Document. Impact Assessment Report. Accompanying the Document Proposal for a Directive of the European Parliament and of the Council on Ambient Air Quality and Cleaner Air for Europe (recast). SWD/2022/545 final.

Hoffmann B, Brunekreef B, Andersen ZJ, Forastiere F, Boogaard H. Benefits of future clean air policies in Europe. Proposed analyses of the mortality impacts of PM2.5 and NO2. Environ Epidemiol 2022;6:e221.

World Health Organization. WHO global air quality guidelines: Particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. Geneva: World Health Organization. 2021.