Briefing Note on New WHO Air Quality Guidelines

Summary

• Poor air quality results in short- and long-term health effects and is responsible for ~ 28  – 36,000 premature deaths each year across the UK.  The key pollutants of concern in the West Midlands today are nitrogen dioxide gas (NO₂) and fine particles in air (PM_2.5).

• Air quality objectives (AQOs) reflect levels considered to be acceptable in terms of protecting human and environmental health; these are established nationally (as a devolved matter in the UK) and are legally binding. 

• The World Health Organisation (WHO) issues guideline levels of air pollutants for the protection of human health. The WHO guidelines are effectively the lowest concentration at which there is clear evidence of an increase in risk to health; they do not consider feasibility or cost.  WHO guidelines are not legally binding, but are an evidence-informed tool for policymakers, and are referenced in the air quality target setting process in the Environment Bill.

• The WHO guidelines were last set in 2005.  Since then, extensive research has found significantly stronger evidence of the impacts of ambient air pollution on human health, including at lower concentrations.  WHO updated their Global Air Quality Guidelines on 22 September 2021. The new update includes interim targets intended to guide reduction, as well as revised guideline levels, including (as annual mean concentrations) :

• PM_2.5     Interim targets of 35 / 25 / 15 / 10, and a guideline level of 5 mg m^-3
  • NO₂ :     Interim targets of 40 / 30 / 20, and a guideline level of 10 mg m^-3

• When averaged to ward level across the West Midlands, modelled annual mean concentrations of PM_2.5 and NO₂ are in excess of the new WHO guideline level in all cases, with roughly 60% and 40% of the region’s population living in wards with average annual mean concentrations of PM_2.5 and NO₂ (respectively) above the next interim target level.

• The new WHO guidelines reflect the science evidence that air pollution harms human health even at low levels. They pose a significant challenge for clean air policy in many urban areas of the UK, and are likely to both increase attention on PM_2.5 levels, and intensify scrutiny on actions to reduce exposure to NO₂, across a wider proportion of the population.