Meeting WHO's air pollution guidelines could save nine million lives

Meeting the World Health Organization's recommended annual guidelines for air pollution resulting from fine particulate matter and nitrogen dioxide has the potential to save more than 9 million lives a year in low- and middle-income countries, say University of Cambridge researchers.

It would also bring substantial savings from reduced illness, including lower healthcare costs and increased productivity as individuals take less time off work resulting from preventable illness.

Outdoor air pollution is the largest environmental threat to human health worldwide. It has been linked to increases in heart and lung diseases, including coronary heart disease, stroke, asthma, chronic obstructive pulmonary disease, and dementia. As well as the burden on individuals and their families, these diseases also have a substantial economic toll in terms of healthcare costs and lost productivity.

Because of the growing body of evidence of the impact of poor air quality, in 2021 the World Health Organization (WHO) revised its air quality guideline values for recommended maximum levels for several pollutants, including fine particulate matter (PM_2.5) and nitrogen dioxide (NO₂).

PM_2.5 is particulate matter with a diameter of 2.5 microns or less, tiny particles small enough that they can be inhaled deep into the lungs. These particles come from several sources, including vehicle emissions, power plants, industrial processes, wood burning stoves and fireplaces, and construction dust. They also form in the atmosphere because of complex chemical reactions involving other pollutants such as sulphur dioxide and nitrogen oxides.

Nitrogen dioxide is one of the key pollutants that arise from burning fossil fuels. It is found in vehicle exhaust emissions, especially from diesel vehicles, and industrial emissions, as well as those from gas stoves and heaters.

The problem disproportionately affects low- and middle-income countries (LMICs), where air quality has generally deteriorated in line with large-scale urbanization, economic development, and increasing use of cars and motor vehicles.

In a paper published today in Environment International, researchers at IMS Epidemiology, University of Cambridge, explored the potential health and economic benefits of improving air quality in 136 LMICs, focusing on PM_2.5 and NO₂.

The team combined detailed data from air pollution, population size and health with published evidence on the links between pollution, mortality and disease. They used computer modelling to estimate how deaths and new cases of illnesses might change if levels of particular pollutants fell to the WHO's recommended air quality guidelines values and the more relaxed WHO interim targets. They also estimated the economic value of reducing the risk of premature death, alongside potential savings in healthcare and productivity costs.

The results suggest that meeting the WHO's guideline levels for PM_2.5 could prevent or postpone an estimated 9.4 million deaths in a single year across the countries studied. Reaching the guidelines for NO₂ could prevent or postpone around 1.1 million deaths*.

Even meeting the less stringent interim targets could lead to substantial population health benefits: around 6.6 million fewer deaths associated with PM_2.5 and 435,000 associated with NO₂.

The potential benefits extend beyond reducing deaths. The researchers estimated that meeting the recommended PM_2.5 levels, could mean 2.8 million fewer new cases of chronic obstructive pulmonary disease, 1.1 million fewer new cases of dementia, 7.3 million fewer new cases of coronary heart disease, and 2.3 million fewer new cases of stroke in a year.

Tackling air pollution is likely to have a huge impact on improving quality of life and reducing the number of early deaths. For the first time, we've been able to model the potential benefits of the WHO's clean air guidelines across countries with the highest levels of outdoor air pollution, both in terms of the millions of lives that could be saved every year and the potential economic and societal benefits."

Dr. Annalan Navaratnam, Clinical Research Fellow at IMS Epidemiology, University of Cambridge

The team showed that there could also be substantial economic benefits, including savings from reduced healthcare spending and productivity losses. For example, meeting the PM_2.5 guidelines could lead to annual direct medical cost savings estimated at $11.8 billion for coronary heart disease, $5.9 billion for stroke, and $8.6 billion for dementia.

By preventing illness and disability, cleaner air would reduce lost work capacity. The PM_2.5 WHO guidelines could lead to estimated annual productivity gains including $17.9 billion for stroke, $18.1 billion for COPD and $5.3 billion for coronary heart disease.

Dr Haneen Khreis, also from IMS Epidemiology, Cambridge, added: "Meeting the WHO's air quality guideline values will not be straightforward, but low- and middle-income countries have a critical opportunity to shape healthier futures as their populations grow and their cities expand.

"Decisions about transport, urban planning and energy can make a real difference to the air people breathe and the diseases they experience. Economic development is essential for these countries, but it need not come at the expense of public health. Having a healthy population is not just a moral imperative; it will almost certainly bring large economic benefits."

The research was supported by UK Research & Innovation (UKRI).