‘It threatens us all’: How dirty air became the world’s silent killer

It’s a staggering figure: with a death toll of more than seven million every year, air pollution kills more people than AIDS and malaria combined.

But it’s not just countries like India, China, or Pakistan– where thick smog regularly envelopes these nation’s largest cities – that are struggling with the fallout from dirty air.

Across all continents, including Antarctica, air pollution has become an inescapable part of modern life.

Emissions from industry, vehicles, cooking, heating, and natural pollutants like dust and sand all play a role.

Just last week, a major study revealed that only seven countries globally meet the air quality standards set by the World Health Organization, leaving 99 per cent of the world’s population at risk of a vast array of health conditions linked to the air they breathe.

But its impacts are not consistent, with vast inequalities between rich and poor.

“Air pollution threatens us all, but the poorest and most marginalised people bear the brunt of the burden,” Dr Tedros Adhanom Ghebreyesus, WHO Director-General, has previously noted.

Financial resources, stringent government actions, and access to safer energy sources all mean that air pollution in Europe and North America has drastically fallen over the last few decades, whilst Asia and increasingly Africa suffer from the highest death rates.

Air pollution is measured in ‘particulate matter’, or PM2.5 – the tiny airborne particles that

are made up of a variety of toxic substances like sulfate, nitrates, ammonia, sodium chloride, and black carbon.

These toxins are about one-thirtieth of the width of a singular strand of hair – so small that, when breathed in, they can lodge themselves in internal organs and penetrate deep into the bloodstream.

Short-term exposure can lead to reduced lung function, respiratory infections, and asthma.

But long-term exposure, of the sort experienced by billions of people worldwide, can cause heart disease, cancer, stroke, and lower respiratory disease, leading to premature death.

The very young and very old are the most vulnerable; 60 per cent of the air pollution-related deaths that occurred in 2019 were among children under 15 years and adults over 70 years, according to the Global Burden of Disease.

A growing body of evidence has also linked exposure during pregnancy to an increased risk of stillbirth; of the two million cases recorded each year, around half are thought to be directly caused by air pollution.

And it’s not just health.

The World Bank estimates that the global economic cost of air pollution-related disease exceeds trillions of dollars annually.

In the UK, the toll on the NHS is thought to be around £20 billion every year, according to the Environmental Research Group at Imperial College London.

But although the developed world certainly suffers, air pollution has gotten much better over the past century. In Britain, emissions of particulate matter have fallen by around 80 per cent since 1950.

There are several reasons. The evolution of fuel standards for car emissions over the past few decades marks a notable triumph; compared to vehicles manufactured in the 1960s, modern cars have about a 95 per cent reduction in tailpipe pollutants like carbon monoxide and nitrogen oxides.

EU directives on emissions and similar policies in other developed nations have helped businesses reduce pollution, and the elimination of lead and drastic reductions in sulphur levels from industry has also helped significantly.

Economic advancement has also meant people in regions such as Europe and America no longer cook or heat their homes using solid fuels like wood and charcoal – a major source of indoor air pollution.

Despite these major improvements, around 98 per cent of Europeans still live in areas the WHO says have unhealthy levels of PM2.5, contributing to around 400,000 premature deaths in the region each year.

Yet low and middle-income countries are grappling with the worst effects, accounting for 89 per cent of global morbidity, says the WHO.

In the developing world, populations are booming: the majority of children born over the next century – 77 per cent – will be in the most resource-limited regions of the world, with over half, around 40 million, born in sub-Saharan Africa.

Industrialisation and urbanisation have increased industrial activities and infrastructure development – from factories to power plants – and are two of the biggest factors causing heightened emissions.

Weak environmental regulations and enforcement further exacerbate the problem, allowing industries to operate without proper emission controls.

For example, agricultural practices such as stubble burning – where leftover crop residue is burned to clear fields after harvesting, pushing vast amounts of toxic black carbon into the air – is banned in much of Europe and North America, but commonplace across Asia and Africa.

Last year, around 38 per cent of New Delhi’s pollution was attributed to stubble-burning activities in the neighbouring states of Punjab and Haryana.

“In low and middle-income countries, lessening the burden of air pollution doesn’t always make it to the top of the list in terms of budgetary priorities,” explained Christi Schroeder, air quality science manager at IQAir, a Swiss company responsible for monitoring air pollution levels globally.

The world’s top three most polluted countries – Bangladesh, Pakistan, and India – are all located in South Asia. The region is also responsible for the world’s 10 most air-polluted cities.

But Africa is not far behind. The continent’s worst affected countries – Chad, Burkina Faso, and the Democratic Republic of Congo – all place in the top 10 most air-polluted nations on the planet, with more African nations expected to join the list over the next decade.

Whilst industrialisation, poor regulation, and a boom in vehicle ownership all play a huge role in outdoor pollution, the developing world also grapples with the added burden of indoor pollutants.

Around 2.3 billion people – mostly located in Sub-Saharan Africa, Latin America, and South Asia – still cook, heat, and light their homes using solid fuels like wood, charcoal, and kerosene. This domestic air pollution kills more than 3.8 million every year in the global south.

“When you burn a solid fuel, it easily produces 20 to 30 times higher amount of air pollution indoors – meaning that people are much more exposed in the home,” explained Dr Peter Kahung Chan, Professor of environmental and cardiovascular epidemiology at the University of Oxford.

In poorly ventilated homes, indoor smoke can have levels of fine particles 100 times higher than acceptable, according to the WHO. Women and children, typically responsible for household chores, bear the greatest health burden.

Natural sources of pollution like sand and dust also cause significant problems, in both developing and developed countries.

Just last week, a dust storm from the Sahara desert blew into southern and eastern Europe, leaving countries including Greece and Malta with a temporary spike in PM.2 – around 10 times the WHO’s recommended level – according to Copernicus, the EU’s air monitoring service.

While much remains to be understood, the assumption among experts is that natural particles like dust and sand can have the same detrimental effects on health as man-made pollutants, explained Dr Jonathon Griggs, Professor of Paediatric Respiratory and Environmental Medicine at Queen Mary University.

Climate change is set to exacerbate the problem.

As temperatures rise and precipitation patterns shift, many regions are becoming more arid and desert-like.

As the Sahara pushes further south, Central and North African countries are beginning to suffer from the fallout.

In 2022, Chad, covered in large part by the Sahara desert, surprised the world by ranking as the most polluted country on earth, with an air particulate matter rate 18 times higher than what the WHO considers safe.

Respiratory illness is already the leading cause of death in Chad, and more than two children die from pneumonia every hour, accounting for nearly a quarter of all child deaths.

Forest fires, which worldwide are burning nearly twice as much tree cover today as they did 20 years ago, are another major source of outdoor air pollution, releasing toxins like carbon monoxide and nitrogen oxides into the air – both toxic to human health.

In Northern California, deaths due to PM2.5 exposure rose by up to 16 per cent during the state’s large wildfires in 2020.

In global terms, air pollution is falling. But the rate is “nowhere near fast enough” to mitigate its effects, argues Dr Chan.

In the world’s poorest regions, its effects are catastrophic. In the world’s richest, they are less severe – but levels are still too high to not deem it a public health crisis.

Dr Schroeder and her team at IQAir are advocating for better global monitoring as a first step in bridging the air pollution gap between rich and poor countries.

There are currently around 30,000 censors worldwide, but they are concentrated in high-income countries.

For example, while New York City has 30 stations tracking its PM2.5 levels, the whole of Mali has just two. Others like Malawi and Sudan have none.

“The fact of the matter is, there is so little air quality monitoring done in places like Africa right now that we don’t know what we don’t know,” said Schroeder.

“The top priority right now is to bridge the gap in monitoring, because nothing can be done until you know what the current state of things is.”

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