Unprecedented emission reductions are needed throughout Europe to comply with the new 2021 World Health Organization (WHO) Air Quality Guidelines, according to a recent article led by scientists from the Barcelona Supercomputing Center (BSC) published in Environmental Research Letters. The study quantifies the increase in the percentage of measurement stations that exceed each new air quality guideline across all the countries reporting air quality information to the European Environmental Agency (EEA).

Air pollution is Europe's most considerable environmental health risk and a significant cause of premature death and disease. Now, thanks to the advances in the research into the human health impacts of air pollution, we know that adverse effects begin at much lower concentrations than previously understood. The latest scientific evidence is reflected in the 2021 WHO Air Quality Guidelines, which represent a significant revision over the previous ones set in 2005. 

The WHO’s new guidelines recommend air quality levels for six pollutants, where evidence has advanced the most on health effects from exposure: nitrogen dioxide (NO₂), particulate matter (PM_2.5 and PM₁₀), ozone (O₃), sulfur dioxide (SO₂), and carbon monoxide (CO). Almost all the 2021 recommended concentrations are significantly more stringent. For the most harmful pollutants, such as NO₂ and PM_2.5, the new annual average limits are 75% lower (from 40 to 10 µg/m3) and 50% lower (from 10 to 5 µg/m3), respectively.

Non-compliance, defined as the percentage of total stations exceeding each pollutant's limits, was already substantial with 2005 WHO’s recommendations across Europe. With the new 2021 guidelines, the BSC study shows dramatic increases in non-compliance, especially for NO₂, PM₁₀ and PM_2,5 (from 8%, 50% and 77% to 88%, 85% and 98%). Across non-compliant stations, the median distance to compliance also jumps significantly (from 16%, 26% and 41% to 120%, 41% and 160%).  For O₃, a new average 6 monthly peak limit is exceeded at 97% of stations.

“The new guidelines set limits at which high confidence exists in the adverse effects on human health. The fact that most European citizens are currently breathing such damaging levels of air pollutants is highly concerning,” said BSC researcher Dene Bowdalo.

Lessons learned from COVID-19 lockdowns

The researchers analysed monitoring data during business-as-usual conditions between 2017 and 2019, before the onset of the COVID-19 pandemic. However, the article also evaluates the impact that emission reductions during COVID-19 lockdowns had on non-compliance to extract some lessons to give scale to the challenge of meeting the new WHO Air Quality Guidelines. 

Decreases in non-compliance were only significant during the most stringent 3-month COVID-19 period (15 March-15 June 2020), especially for NO₂, which is mainly produced by diesel engines. However, despite an average reduction of 32% in road transport activity during 2020, more than 50% of stations that measure NO₂ across Europe remain non-compliant. This implies that radical measures, such as zero-emissions zones, or the ban on the sale of fossil fuel vehicles, would be needed to reduce concentrations in line with the current WHO recommendations sufficiently.

“Despite the dramatic changes to transport and industry through the COVID-19 lockdowns, we were still nowhere near meeting the guidelines for many pollutants. This evidences that only radical actions to alter the current structures of our urban areas will be able to reduce the levels of air pollutants sufficiently,” said Bowdalo.

Compliance with the new WHO guidelines is estimated to prevent 66% of premature deaths attributed to PM_2.5 exposure in Europe. These numbers will naturally apply more significant pressure on the EU to revise its standards. EU standards have consistently lagged decades behind the WHO guidelines, but countries still frequently exceed limits despite this. For even more ambitious means to be effective, they should be accompanied by supporting concrete measures so that the transition does not leave anyone behind.

This is particularly important for countries with lower income, typically exposed to higher pollution levels but depend on polluting energy sources or those disproportionately affected by natural emission sources. Some air pollutants are also short-term climate forcers (e.g. black carbon), and several win-win mitigation policies can improve both air quality and mitigate climate change at a potentially lower intervention cost.

The legislative proposal for the revision of the EU's standards is scheduled at the tail-end of 2022, and the factors outlined in this work need to be carefully considered by the EU before any new standards are set. 

Reference: Dene Bowdalo et al. (2021). Environ. Res. Lett. https://doi.org/10.1088/1748-9326/ac44c7