“It’s safe to say, there are no safe levels of air pollution”

By Dr Gary Fuller, Imperial College London

Pressure is mounting on the Westminster government to put the World Health Organisation’s (WHO) air pollution guidelines into law. For example, Philip Barlow, the corner who investigated the death of Ella Adoo Kissi-Deborah included the adoption of WHO standards in his prevention of future deaths report and two months ago, the British Medical Association, more than 20 nursing colleges, the Lancet and the British Medical Journal added their voices in an open letter to government.

Many legal limits for air pollution already reflect WHO guidelines with the notable exception of PM2.5 particle pollution where the current non-binding target is twice that recommended by the WHO. This pollutant, in combination with nitrogen dioxide, was linked with the majority of the estimated 28,000 to 36,000 early deaths from air pollution in the UK in 2013.

Would adoption of the current WHO guidelines be the best way forward or does the health evidence suggest a new approach? Legal limits on poor air have been in place across the UK and Europe since the 1980s and have been revised each decade or so but we continue to struggle with this issue.  Simply including an annual limit for air pollution in law has the very strong advantage of being easy to understand and easy to measure, given sufficient high-quality measurement equipment. Campaigners have also had some success at holding government accountable when limits are not met; Client Earth’s legal cases against the UK government on nitrogen dioxide for example.

However, the health evidence has moved on since the WHO guidelines were created in 2005. New health studies are emerging from locations where people already breathe air that meets the guideline values. The health impacts of these exposures are the theme of research projects being funded by the US Health Effects Institute. One looked at the air pollution and health records of 61 million people in the US who receive Medicare (Quian et al. 2017) and the another focused on nearly 9 million Canadians (Brauer et al. 2019). The headline finding in both studies was that there was no evidence of a safe threshold for PM2.5. A study across 652 cities around the globe has reached the same conclusion. This implies that any and every reduction in exposure would improve health.

New WHO guidelines are expected this autumn. The shape of these is not known at the moment, but it is clear that working toward a legal limit does not mean that air pollution will improve for everyone. Instead, it can focus effort in the worst polluted areas and does not motivate improvements in other places. Worse still, the mis-framing of the limit as a safe threshold, rather than a way point on the path to cleaner air, can have undesired outcomes. For example, professional guidance for UK local planning and development creates barriers to building a polluting development, say a new car park or factory, in an area that does not meet legal limits for air pollution, but it suggests that adding small amounts of air pollution in areas that meet legal limits may be of “negligible” significance.  

It would be better to aim for downward trends in air pollution everywhere. For instance, the Canadian government’s guidance on air zone management requires locations that already meet limits to work to adopt a process of “continuous improvement” and to “keep clean areas clean”. So, instead of achieving limits should we focus on the way that air pollution is changing? Two studies in London (Font el at. 2016, 2019) have looked at rates of change rather than limit value compliance.  Re-framing the question in this way showed that the policies in place between 2005 and 2016 led to rapid decreases in some locations but did not lead to improvements in air pollution everywhere. Some streets even had increases. This was especially the case in outer London. A further study (Barnes et al. 2019) found that the gap between traffic air pollution breathed by the richest and poorest in the UK widened in the first decade of this century. Focusing on change, and importantly creating feedbacks within agile policies, might have prevented this.

This idea is not new. For instance, John Spitzer Owens analysed UK air pollution data using this approach in 1936, long before limits on the quality of outdoor air were adopted into law. In 2007, the Royal Commission on Environmental Protection recommended holistic targets to reduce air pollution exposure. Current UK law and EU Directives set targets for decreasing the average air particle pollution across each country. But this allows deteriorations in some areas to be traded-off against improvements in other locations. So yes, health evidence suggests that meeting WHO guidelines in the UK would reduce the health impacts of air pollution, but the same evidence also suggests that we also need to go further and focus on the rate of change to achieve improvement in air pollution for all communities. There are no health thresholds for any of the common air pollutants or put another way, it’s safe to say there are no safe levels of air pollution.

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