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expert reaction to new global air quality guidelines

The World Health Organization (WHO) have published new global air quality guidelines.


Prof Frank Kelly, MRC centre for Environment and Health at Imperial College London, said:

“Air pollution is the biggest environmental threat to human health accounting for 7 million premature deaths every year. The new WHO guidelines, the first update since 2005, provide an update on the damage air pollution inflicts on all ages across the life course. Concerted action to meet the updated guidelines will save lives and reduce the burden of disease.

“The fact that many of the guidelines have been tightened since 2005 demonstrates how evidence of the health impacts of poor air quality has increased in severity and scope in the intervening years. Harms to health occur throughout the entire life course, but pregnancy and childhood are especially vulnerable periods—with mounting evidence for effects on long-term growth and cognitive ability. Moreover, the report devotes an entire chapter to the most vulnerable in society; the risks of air pollution are not evenly distributed, and those living in areas of deprivation are especially at risk.

“Meeting these updated WHO air quality guidelines will be a challenge, especially in many UK cities, but by not doing so will mean our children and generations to follow will suffer from our inaction. Meeting these guidelines will require international co-operation; reducing emissions of pollutant pre-cursors and transboundary pollution that travels across continents. Importantly, many of the necessary actions will have additional benefits toward limiting climate change, resulting in a healthier planet and a healthier population.”


Prof Alastair Lewis, National Centre for Atmospheric Science at the University of York, said:

“The new air quality guidelines from WHO dramatically increase the scale of challenge to society if it is to reduce air pollution to concentrations which would not cause significant public health harms. Some of the new guideline values look feasible for the UK to meet, certainly within perhaps a decade or so, if clean technologies work as hoped and implementing net zero progresses at pace. Nitrogen dioxide (NO2) for example is already starting to fall as older vehicles retire and battery electric vehicles increase in number; there is the prospect of largely eliminating this as a cause of harm in the medium to long-term. 

“However the new WHO guideline values for fine particles (PM2.5), perhaps the most contentious and high profile of all air pollutants, look close to impossible to achieve in some urban areas of the UK, Europe and Asia.  Particle pollution is very complex and comes from natural sources as well as from transport, energy, industry and our homes. PM isn’t just emitted directly from tailpipes or chimneys, it can also be formed in the air from complex chemical reactions involving other pollutants, like ammonia from agriculture or organic chemicals from domestic products.  Once emitted particles can reside in the atmosphere for up to weeks at a time and so drift between nations, adding to the challenge. The southeast of England for example is significantly impacted by PM pollution from the near continent. Even if the UK was an uninhabited island, that corner of the country would likely experience annual PM2.5 concentrations higher than WHO now recommend. 

“There is however still a huge amount that can be done to improve air quality and reduce emissions, for example eliminating remaining fossil fuel power stations, tackling unnecessary solid fuel burning in homes, and removing polluting older vehicles. Every journey made by bike or foot rather than car reduces emissions and improves air quality.  But PM2.5 is to an extent also an inevitable and unavoidable consequence of living a 21st century life. Even the newest electric vehicles still generate particles from the friction of their wheels on the road; substantial amounts of PM2.5 are emitted from seemingly mundane activities like cooking food. 

“The unenviable challenge for policymakers will be to respond in a way that minimises the proven harms to health, as set out by WHO, but with policies that are proportionate, cost effective and crucially deliver benefits equitably across the country and population. Whilst we have become used to the idea of a future with ‘net zero’ greenhouse gases, there can really never be a world of ‘zero’ PM2.5; so the question is really how low can we feasibly go? In this in mind the new WHO guidelines could, for some, be fundamentally beyond reach, even including countries like the UK that start the advantages of wealth, an island geography and a favourable wet and windy climate.”


Prof Roy Harrison FRS, Professor of Environmental Health at the University of Birmingham, said:

“The WHO has followed the science which now shows adverse effects of nitrogen dioxide and fine particle (PM2.5) exposure at well below the 2005 guideline levels.  While countries such as the UK were within close proximity to meeting the old guideline levels for these pollutants (those most important for public health), and many people were arguing for a commitment to compliance, the new guidelines will not be achievable for decades, if at all.  The adoption of electric vehicles will lead to a dramatic improvement in nitrogen dioxide, provided a solution can be found for heavy goods vehicles, but will do little, if anything for PM2.5 due to the dominance of non-exhaust particles from brakes, tyres and the road surface over exhaust emissions.  Around 3 micrograms per cubic metre of PM2.5 in southern England is from natural sources, leaving little headroom for emissions from human activity in meeting a guideline of only 5 micrograms per cubic metre.  It is also worth noting that emissions in continental Europe make a substantial contribution to PM2.5 levels in the UK, so we depend very much upon effective action in other countries.  Nonetheless, I very much welcome the emergence of these challenging guideline levels, and hope that governments around the world will adopt them as long-term targets with a clear timetable for achievement.”


Dr Audrey de Nazelle, Senior Lecturer and outgoing Network of Excellence on Air Quality chair at Imperial College London:

“Imperial’s Network of Excellence on Air Quality expresses support for the new guidelines, and strongly encourages the UK government to take ambitious actions to reduce air pollution everywhere and as soon as possible.

“The new guidelines come at an opportune moment in the UK for the adoption of stricter standards to become embedded in the Environment Bill. Now is the time for UK politicians to show by their vote that they understand the gravity of air pollution impacts and to take urgent and bold action, reflecting the new updated WHO guidelines that protect our health.

“The new WHO guidelines send an unequivocal message that everyone everywhere will benefit from reducing air pollution. New legislation is needed to encourage air pollution reductions everywhere, and not just in pollution hot spots, to achieve healthy air quality for all, and the Environment Bill is an opportunity to do that.

“Every sector should contribute to this improvement. Politicians need to take bold action to enable transitions away from fossil fuel, car reliance, inadequate agricultural and industry practices and unstainable consumption patterns. The WHO publication is also an opportunity to fully embrace transitions towards economic, social and environmental sustainability.

“Society will benefit in multiple ways from ambitious government action to reduce air pollution, including from reducing greenhouse gases to help mitigate climate change, and promoting more liveable cities where healthy behaviours are encouraged.

“We also support the joint statement regarding the Guidelines issued by the International Society for Environmental Epidemiology (ISEE) and the European Respiratory Society (ERS) and endorsed by more than 100 medical, public health and scientific societies. This statement, for which I am a co-author, proposes concrete ways in which legislation should advance and urges governments to implement bold and ambitious clean air policies without delay in order to protect health and wellbeing.”


Dr Daniela Fecht, Lecturer in Geospatial Health from the School of Public Health at Imperial College London:

“Air pollution poses a great risk to human health: it is linked to major lung and heart diseases, diabetes, cancer, premature mortality and emerging evidence points to adverse effects on pregnancy, cognitive development in children, dementia and mental health, as well as risk of dying from COVID-19. Air pollution ranks fourth among major risk factors for global disease and mortality. In the UK, it contributes to between 28,000 and 36,000 deaths annually, and often hits ethnic minorities and deprived communities the hardest.”


Dr Ben Barratt, Reader in Environmental Exposures & Public Health and incoming Network of Excellence on Air Quality chair at Imperial College London:

“As this long-awaited update demonstrates, evidence of the scope and severity of the health and economic impacts of air pollution in the UK and across the world has strengthened in recent years. We know what actions and policies are needed to improve quality of the air we breathe; we now need to accelerate their implementation with greater ambition and urgency.”


Dr Stefan Reis, Head of Atmospheric Chemistry and Effects, UK Centre for Ecology and Hydrology (CEH), said:

“For fine particulate matter, data for 2018 from the Automatic Urban and Rural Network (AURN)[1] shows annual mean concentrations between 4 µg m-3 in remote rural areas in the north of Scotland and 16 µg m-3 at London’s Marylebone Road. Annual mean nitrogen dioxide concentrations ranged from 4 µg m-3 (Eskdale Muir) to 85 µg m-3 (Marylebone Road). With the new AQG setting annual mean values of 5 (PM2.5) and 10 (NO2) µg m-3, substantive efforts aiming at emission reductions especially in air pollution hotspots and across key emission sources would be required, if the AQGs would be translated into legally binding limit values.

“A growing body of scientific evidence, including a major WHO-led review, has shown that air pollution guidelines required updating. New research indicates long-term exposure to even lower concentrations of fine particulate matter below current limits can have negative health effects, including brain health2,3,4,5. This means a focus on bringing down high levels of air pollution at only selected hotspot locations is not sufficient to address public health effects at a wider, population level.”



Declared interests

Prof Harrison: I offer scientific advice to Defra as a member of the Air Quality Expert Group, and to DHSC as a member of the Committee on the Medical Effects of Air Pollutants, and was a member of the WHO panel which recommended the 2005 guidelines.

Prof Reis: No interests

Prof Lewis: No conflicts to declare beyond receipt of funding for research from UKRI sources and UK government. I am currently Chair of the Defra Air Quality Expert Group, which provides advice on air pollution issues to the UK government, however these comments are made in a personal capacity. 

No others received.

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