In a milestone moment, WHO today issued new guidelines for a range of health-harmful air pollutants – recommending a reduction by one-half in safe levels of fine particulates (PM2.5) – considered to be the benchmark indicator of health impacts that lead to some 7 million deaths a year. 

The new standards put most cities of the world – including in high income countries – in excess of WHO clean air standards once again – after a decade in which many cities and countries enacted strict new policies to clean up their air in line with the last set of WHO recommendations, issued in 2005.  

But reducing ambient concentrations of PM2.5 pollution, both outdoors and inside homes, even further to the new guideline limit of 5 micrograms per cubic meter (5 µg/m3) would save some 5-6 million lives a year, said WHO expert Michel Kryzanowski at a WHO press launch of the new guidelines on Wednesday. And that justifies the strict new WHO recommendations. 

“Some 80% of health impacts could be avoided if we get to these WHO levels globally,” Kyrzanowski said. “It’s not because the pollutants became more dangerous, but we know much more about how those pollutants affect human populations.” 

Altogether, the new WHO guidelines impose stricter limits on five key pollutants overall – including nitrogen dioxide, ozone and carbon monoxide, as well as small (PM10) and fine (PM2.5) particulates.

The new limits reflect new scientific evidence that has documented the even greater impacts of air pollution from respiratory and cardiovascular diseases, stroke and cancers, and the risk of severe COVID-19, said WHO Director General Dr Tedros Adhanom Ghebreyesus in his remarks. 

“Right now, the simple act of breathing contributes to more than 7 million deaths a year,” Dr Tedros said. Those health impacts extend from “the brain to a growing baby in a mother’s womb, at even lower concentrations than previously observed”.”  

And air pollution is a particular health threat in low-income countries – where millions of people routinely breathe air choked with pollutants that are many times over WHO guideline levels “due to urbanization and rapid economic development, and household air pollution in the home caused by cooking, heating and lighting.” 

Less Climate Change – More Economic Growth &  Benefits for Developing Countries  

Along with saving lives, stricter limits on air pollution emissions will translate immediately into less climate change as well as generating trillions of dollars of economic benefits, stressed Tedros, in his appearance alongside WHO European Regional officials, who oversaw the new guidelines development, and WHO’s director of Climate,, Health and Environment, Maria Neira. 

“These guidelines come at an important time ahead of the COP26 climate change conference in November. .. I urge all countries to put these guidelines to use to save lives, support healthy communities and help address the climate crisis,” Tedros said. 

Added Hans Kluge, WHO Europe Regional Director, “almost all efforts to improve air quality can enhance climate action: almost all climate change mitigation efforts improve air quality, with immediate health benefits… “This enhances return of investments into measures that simultaneously address both.”

Not only would millions of lives be saved, but some US$ 3.5 trillion a year in lost worker productivity and healthcare costs could be avoided if the new WHO guidelines were met, added Neira.  Other benefits would extend to agricultural production, whose yields are reduced by pollutants like ozone, which develops over cities and then drifts across the countryside. 

Key sources of pollution that could readily be identified and reduced range from energy and transport systems to industrial pollution, waste burning and household pollution from wood and coal fire use, she noted.  All require a “holistic approach” by policymakers to tackle and reduce.

New limits – a high bar to reach 

But even in developed countries, with comparatively good air quality, the stricter limits will be a high bar to reach.   Many cities in Europe and North America have average annual air pollution concentrations that meet the current WHO guideline limits for the benchmark pollutant of PM2.5, or come close.  

Those cities and towns will now find themselves far out of compliance with the new WHO standards – not to mention low- and middle-income cities in regions such as South East Asia, which suffer from chronic air pollution levels that may be 10-20 times higher than WHO guidelines. 

“Almost all guideline levels are now lower than 15 years ago. We know that for many countries, this places the bar even higher than ever before,” Kluge said. “But these guidelines also provide interim targets, to support stepwise progress towards that achievement.”

Nitrogen dioxide pollution, associated with diesel vehicles, reduced four-fold 

Along with the tighter limits on PM2.5 – most closely associated with fatal health impacts – the new WHO guidelines also recommend a fourfold reduction in average annual concentrations of nitrogen dioxide – from 40 µg/m3 to just 10 µg/m3. 

Recent evidence has underlined the long-term damage that NO2 exposures can wreak on respiratory systems – from a very young to older ages. NO2 also contributes to the production of urban ozone (O3) – which is a short-lived climate pollutant (SLCP). Reducing short-lived climate pollutants, including black carbon particulates and methane, as well as ozone, would be one of the fastest ways to slow down the pace of global warming, say advocates with the Climate and Clean Air Coalition, sponsored by the United Nations Environment Programme and supported by WHO.  

But the strict new NO2 limits also strike at the heart of the diesel car industry, which had built a generation of vehicles with progressively lower emissions of PM2.5 – but still high emissions from nitrogen dioxide – which particulate filters cannot trap.  

Closer adherence by cities to the new WHO NO2 guidelines would thus almost certainly hasten the transition to hybrid gasoline and  electric vehicles – as well as other public transit, walking and cycling alternatives.    

At the same time, the new WHO guidelines also establish, for the first time ever, a limit for “peak season” concentrations of ozone, as such. Ozone contributes to chronic respiratory disease, including the prevalence of asthma, as well as inflicting considerable damage on crop production when ozone drifts from cities into surrounding rural areas.  

SO2 guideline value loosened – but that was due to methods change 

Conversely, however, WHO actually raised its safe guideline for 24-hour concentrations of sulphur dioxide, SO2 – from 20 to 40 µg/m3. A key source of SO2 emissions is industry smokestacks which were among the first targets for air quality campaigns by environmental groups in the 1960s and 1970s. . 

In fact, there is “vast new evidence which was produced in the last 15 years, which confirms what we knew before about sulfur dioxide exposure -that it is producing health effects, up to the very low levels,” said Kryzanowski. 

However, he said methods changes in attributing health impacts to various pollutants still led to a higher baseline indicator for SO2 – in comparison 2005 value, as well as in comparison to the other pollutants now being measured. 

“There was a methodology of setting guidance, which was different back in 2005,” Kryzanowski said. “We tried to make the guidelines comparable between various pollutants. 

“And using the same methodology, the same protocol of defining the guideline values, this protocol ended up actually with a higher value than before. This value  is believed to count the health effects to the same extent as the guidelines for other pollutants, so we believe that it is fair to have it in this form as it is now.” 

Image Credits: Rashed Shumon, WHO, World Bank, Flickr.