Tag: Air Quality Policy

Image credit: Photo “Friends of the Earth 24” by Friends of the Earth Scotland, Flickr, is licensed under CC by 2.0.

By Brodie Walker

Introduction

In 2022, the Scottish Government commissioned a review to examine whether current levels of ambient air pollution, relatively low by international standards, continue to pose measurable risks to population health. The work was undertaken to inform the Cleaner Air for Scotland 2 (CAFS2) Strategy and support alignment with the World Health Organization’s 2021 Air Quality Guidelines. The review was conducted by an interdisciplinary team from UWE Bristol affiliated with the Air Quality Management Resource Centre and the Centre for Public Health and Wellbeing, and the final report was published in October 2023.

An aim of the review was to assess health impacts in countries with ambient air pollution levels comparable to Scotland. This focus arose from earlier CAFS2 work, which identified an apparent absence of association between air pollution exposure and cardiovascular disease in Scottish studies compared with the wider international evidence. To explore this, we undertook a robust, rapid review examining health effects at low concentrations and potential methodological and contextual explanations for these differences.

Health impacts observed at low levels

The review identified strong and consistent associations between low‑level exposures and a wide range of health outcomes:

• Cardiovascular disease: Evidence from countries with ambient pollution levels comparable to Scotland indicates increased risks of cardiovascular outcomes, including stroke and ischaemic heart disease, at PM₂.₅ concentrations well below current guideline values. The absence of these findings in the Scottish studies is likely an artefact of study design and data.
• Respiratory outcomes: Low‑level exposures are associated with worsening asthma, impaired lung development in children, and increased exacerbations of chronic respiratory conditions, even where average concentrations are relatively low.
• All‑cause mortality: Multiple cohort studies report elevated all‑cause mortality risks across the exposure range, including at the lowest observed concentrations of PM₂.₅.
• Birth outcomes: Associations with adverse birth outcomes, including preterm birth and low birth weight, have been detected at low NO₂ and PM₂.₅ concentrations, suggesting sensitivity during early life.
• Neurological and mental health outcomes: Emerging evidence points to associations between long‑term exposure to low‑level air pollution and outcomes such as cognitive decline, dementia, and poorer mental health and well‑being, although causal mechanisms remain an active area of research.
• Other outcomes: Evidence for outcomes such as diabetes and cancer at low pollution levels is more limited and variable, though observed associations may still be important at a population level.

No evidence of a “safe” threshold

A central finding is the lack of any reliably identifiable threshold at which the harmful effects of air pollution cease. For PM₂.₅, large cohort studies demonstrate linear or near‑linear concentration‑response relationships extending to very low exposure levels. The slope of these associations often remains steep at the lower end of the distribution, indicating that marginal reductions in exposure can still produce public health benefits.

Low levels of pollution does not mean low inequality

Although national average levels of air pollution in Scotland are relatively low, the review highlights the importance of spatial variability in exposure and the methodological challenges this presents in low‑pollution settings. Limited exposure contrasts and greater potential for exposure misclassification, particularly for traffic‑related pollutants such as PM₂.₅ and NO₂, may reduce the ability of studies to detect associations when analysing population‑level averages. While the review does not explicitly focus on social inequalities, these considerations are consistent with a wider evidence base suggesting that uneven exposure patterns and population vulnerability may contribute to under‑estimation of health effects.

Implications for public health policy

One of the review’s most important implications is that air quality policy remains highly relevant in low‑pollution contexts. Achieving compliance with existing standards should be viewed as a baseline rather than an endpoint.

In Scotland, annual CAFS2 progress reports published in June 2024 and June 2025 confirm continued nationwide compliance with statutory air quality objectives, while recognising that meeting these limits does not imply the absence of health risk (Scottish Government, 2024; Scottish Government, 2025a). Full enforcement of Low Emission Zones (LEZs) has now been extended across all four major Scottish cities, with early evaluations demonstrating substantial improvements in air quality. Monitoring data indicate a 34% reduction in nitrogen dioxide concentrations within Glasgow city centre following full LEZ enforcement between 2023 and 2024 (Glasgow City Council, 2025).

At a strategic level, the Scottish Government has initiated preparatory work towards a new Air Quality Delivery Framework for Scotland, planned to replace CAFS2 after 2026. In the UK, the Environment Act (2021) continues to drive legally binding commitments, including new, more ambitious PM₂.₅ targets for England.

Conclusion

The review, together with the wider international evidence base, demonstrates that low‑level air pollution continues to produce detectable adverse health effects and that further reductions in concentrations are likely to deliver measurable population health benefits. For policymakers and stakeholders, this reinforces the need to view air quality not simply as a matter of regulatory compliance, but as a continuing public health challenge, even in low‑pollution contexts.

References

Scottish Government (2023a) Health impacts of low‑level air pollution: review and assessment of the evidence. Edinburgh: Scottish Government. Available from:
https://www.gov.scot/publications/review-assessment-evidence-health-impacts-low-level-pollution-countries-levels-ambient-air-pollution-comparable-scotland/
[Last accessed 9 April 2026].

Scottish Government (2023b) Summary report: review and assessment of the evidence on health impacts of low‑level air pollution in countries with ambient concentrations comparable to Scotland. Edinburgh: Scottish Government. Available from: https://www.gov.scot/publications/summary-report-review-assessment-evidence-health-impacts-lowlevel-pollution-countries-levels-ambient-air-pollution-comparable-scotland/documents/
[Last accessed 9 April 2026].

Scottish Government (2024) Cleaner Air for Scotland 2 strategy: progress report. Edinburgh: Scottish Government. Available from:
https://www.gov.scot/publications/cleaner-air-scotland-2-strategy-progress-report/
[Last accessed 9 April 2026].

Scottish Government (2025a) Cleaner Air for Scotland 2 strategy: progress report. Edinburgh: Scottish Government. Available from:
https://www.gov.scot/publications/cleaner-air-scotland-2-strategy-progress-report-2/
[Last accessed 9 April 2026].

Scottish Government (2025b) Air quality policy update: Scottish Air Quality Annual Seminar 2025. Edinburgh: Scottish Government. Available from:
https://www.scottishairquality.scot/sites/default/files/publications/2025-04/Air_Quality_Policy_Update_Andrew_Taylor.pdf
[Last accessed 9 April 2026].

Glasgow City Council (2025) City centre air pollution drops by a third following LEZ enforcement. Available from:
https://www.glasgow.gov.uk/13535
[Last accessed 9 April 2026].

HM Government (2021) Environment Act 2021. London: The Stationery Office. Available from:
https://www.legislation.gov.uk/ukpga/2021/30/contents/enacted
[Last accessed 9 April 2026].

Department for Environment, Food & Rural Affairs (Defra) (2025a) Air pollution in the UK 2024: compliance assessment summary. London: Defra. Available from:
https://www.gov.uk/government/publications/air-pollution-in-the-uk-2024/air-pollution-in-the-uk-2024-compliance-assessment-summary
[Last accessed 9 April 2026].

Department for Environment, Food & Rural Affairs (Defra) (2025b) Air pollution in the UK 2024. London: Defra. Available from:
https://assets.publishing.service.gov.uk/media/68da4202c487360cc70c9e4f/air_pollution_uk_2024_issue_1.pdf
[Last accessed 9 April 2026].

World Health Organization (2021) WHO global air quality guidelines: particulate matter (PM₂.₅ and PM₁₀), ozone, nitrogen dioxide, sulphur dioxide and carbon monoxide. Geneva: World Health Organization. Available from:
https://www.who.int/publications/i/item/9789240034228
[Last accessed 9 April 2026].