London’s Great Smog of December 1952 was the largest in a series of “pea soupers” which brought normal activity to a halt across the capital. The smog lasted from December 5 to December 9 and led to a large spike in hospital admissions and as many as 12,000 deaths.
Pollution episodes like this one were driven by smoke from burning coal in city centres to generate power and heat homes (as recently as the 1980s power plants were still found right in the centre of London). This was then exacerbated by cold and windless winter weather: smoke + fog = smog. This was a very visible challenge. The ensuing Clean Air Acts focused on removing these key pollutant sources to make the air cleaner.
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The air we breathe today looks, and is, much cleaner than in 1952 but is still not clean enough. Poor air quality still contributes to somewhere between 26,000 and 38,000 early deaths each year in the UK, mostly through impacts on circulatory and respiratory health. The resultant costs to healthcare and business have been said to amount to £20 billion every year. This does not include the costs of reduced quality of life or health conditions where links to pollutant exposure have emerged in recent years (including cognitive decline and dementia).
Pregnant women, children and the elderly are more vulnerable to harm, even if their exposure is the same as other population groups. Most health harms are caused by long-term exposure to fine particles (so-called PM2.5) – less than 30 times the diameter of a human hair and invisible to the naked eye.
The latest UK Chief Medical Officer’s Annual Report suggests we need to go further to reduce air pollution and protect health. Importantly, the report highlights advances in our knowledge of the sources, distribution and health impacts of air pollution which can inform evidence-based actions.
What we now know
Although the health risks of pollution were recognised early in the industrial revolution (gravestones in the early 19th century reported “fog-related deaths”) our understanding of these harms has advanced in recent decades.
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Now, 70 years on from the London smogs, we know that health harms exist even at low pollutant levels and that there is no “safe” level of PM2.5 exposure. We also now understand the relative contribution of different pollutant sources to ambient pollution, including road transport, industry and agriculture (due to ammonia emitted from manure and fertiliser). We are also able to better determine where pollutants originated, enabling targeted approaches to reducing them at source. The report also recognises major gaps in our knowledge, including air pollution in indoor environments.
The Chief Medical Officer’s report sets out a need to focus air quality improvements on the places where people live, work and study. This approach recognises that many of these are public spaces, both indoors and outdoors. People there are exposed to air pollution but can do little about it individually, so society needs to act.
Outdoors, the report recommends continuing electrification of transport and technical measures targeting emissions from heavy goods vehicles and car brakes and tyres wearing down (which, perhaps surprisingly, is now a bigger source of particle pollution than exhausts).
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Industrial emissions have fallen substantially, but those from agriculture have not: simple changes in fertilisation approaches are needed. Town planning should support reducing air pollution concentrations and exposure and encourage travel on foot and by bike. In urban areas, burning wood can worsen local air quality. Indoors, the optimal balance between ventilation, energy use and heat loss is a priority for reducing air pollution, preventing respiratory infections and achieving net zero.
Our work in the West Midlands is an example of how these advances can support evidence-based clean air solutions. For example, our research quantifies “real-world” pollutants emitted from vehicles while being driven on Birmingham’s roads, as opposed to being tested in a laboratory that simulates driving conditions. We can also identify the chemical fingerprint of particles in the air to quantify these different sources. We can simulate future air quality changes expected from a given policy, such as specific traffic changes, and calculate the health benefits in terms of deaths and disease diagnoses avoided among a given population.
New air quality targets
Exactly 70 years on from the deadly London smog, we are again on the verge of new legislation to protect people from the harms of air pollution. The Environment Act 2021 enables the government to set new targets for outdoor pollution levels. If sufficiently ambitious, the new targets should balance improvements in the most polluted areas with achieving some benefit for everyone, even if air quality already meets the threshold value.
We now have an opportunity to improve air quality and health through policy choices informed by evidence. Many of these policies will also deliver benefits for the climate, since many air pollution sources involve burning fossil fuels. However, while reducing carbon emissions is a global challenge, air pollution is less dependent on action taken elsewhere. In many cases it doesn’t really matter what the next country or even the next town is doing – the benefits of local actions in terms of human health, reduced inequality and improved lives are clear.
