I’m lucky to have grown up with far cleaner air than my parents or grandparents did. In fact, air quality in the United Kingdom is now better than it was for several generations.¹ Take a look at the charts below, which show the centuries-long trajectory of two key pollutants in the UK.

For younger generations in many other countries, this is not the case. Those living in cities like Delhi, Dhaka, or Accra breathe in some of the most polluted air in their country’s history. This has a huge impact on people’s health: outdoor air pollution leads to millions of premature deaths every year.

If you look at it over time, you find that air pollution tends to follow a very standard pattern as countries develop and get richer.² It’s roughly as you see in the charts: an upside-down U. Outdoor pollution starts low, then climbs as countries burn more fossil fuels for energy and industrialize their economies. Eventually, this reaches a turning point, and emissions fall.

So, we could expect that all countries will go through this transition naturally, just like the UK and many other rich countries did. The problem is that this process took a long time: centuries, in fact. If it takes the rest of the world just as long, billions of people will be exposed to high levels of air pollution for most of their lives. Hundreds of millions will die prematurely due to air pollution.

But it doesn’t have to be this way. Today, we have better technologies and a much better understanding of how to tackle air pollution than we did 50 or 100 years ago. This means people around the world can accelerate this process if they put the right policies and interventions in place.

In this article, I want to focus on the two pollutants shown above: sulfur dioxide and nitrogen oxides. These are two of the four gaseous pollutants included in the World Health Organization’s Air Quality Guidelines.³ This is because they have not only direct impacts on human health but also form secondary pollutants, such as small particulates, which make respiratory and cardiovascular health problems even worse.

By looking at how countries like the UK cleaned up their air, we can better understand how others can do the same, but faster.

How countries reduced emissions of sulfur dioxide — and acid rain

Acid rain was one of the biggest environmental problems of the late 20th century. Here’s the opening of an article in the New York Times in 1979:

“The rapid rate at which rainfall is growing more acidic in more areas has led many scientists and governmental officials to conclude that acid rain is developing into one of the most serious worldwide environmental problems of the coming decades.”

But it’s a problem we hear very little about in Europe and North America today. That’s because it’s an environmental problem we’ve solved.

Acid rain is mostly caused by emissions of a gas called sulfur dioxide (SO₂).⁴ SO₂ can dissolve in water, making rainfall acidic, which damages ecosystems such as forests, soils, rivers, and lakes.⁵ It’s also the reason why you often see historical statues with faces that look like they’ve melted or buildings with fine designs that look like they’ve been washed away. The faces of Kings, Queens, and Saints — made from marble or limestone — break down and dissolve.

The main source of SO₂ is coal burning, whether for electricity, heat, or industrial processes. Coal contains small amounts of sulfur, which is released into the atmosphere as sulfur dioxide when it's burned.

To stop acid rain, you need to stop this sulfur being emitted. There are two ways to do this:⁶

• Burn less coal.
• Install technologies on coal plants which remove the sulfur from the smokestacks before it is emitted into the atmosphere: this is called “scrubbing” or “flue gas desulfurization”.

The United Kingdom did a mix of both. Its coal burning has fallen rapidly since the 1960s. Look at the two charts below: by 2022, coal consumption had fallen by 96% and sulfur dioxide emissions by more than 99%.

The same is true for other countries.

We can see this by looking more closely at the different rates at which these two measures declined. In the chart below, you can see the relative change in coal consumption and SO₂ emissions since 1980 in four countries. In the UK, you can see that both lines dropped, but the reduction in SO₂ happened at a faster rate and continued to fall during periods where coal consumption was stagnant, such as the early 2000s. This is because the UK implemented “scrubbing” technologies.

This difference is even starker in other countries. In the United States, SO₂ emissions declined from the 1980s to the early 2000s while coal use increased. In Italy, emissions had fallen by more than 90% before coal use started to fall significantly.

In these cases, too, countries installed “scrubbers” on their coal plants to capture the sulfur in the smokestack. The implementation of these technologies was initially driven by political action.

In 1990, the US included a cap-and-trade scheme on SO₂ as part of its Clean Air Act Amendments.⁷ The goal was to cut the country's emissions in half by 2010 compared to 1980. Each coal plant was given an “allowance” for how much SO₂ it could emit, forcing it to either implement technologies to reduce its emissions, trade credits with other plants, or pay a large fine for every tonne of extra sulfur it emitted. It was clearly successful and even exceeded its goal: as you can see in the chart, SO₂ emissions in the US had dropped by almost 80% by 2010.

European countries were under similar pressure to reduce emissions after targets were set within the region’s Convention on Long-range Transboundary Air Pollution, which was set in 1979. That’s why you see the rapid drops in the UK, Italy, Germany, and others throughout the 1980s, ‘90s, and 2000s.

Step outside of Europe and North America, and we can see the approaches of different countries in tackling these emissions. In the chart below, I’ve shown the same data for the UK and the US, but China and India have been added for comparison.

China’s trajectory makes it very clear that reducing coal consumption is not the only way to reduce SO₂ emissions. Emissions peaked in 2006 and have dropped rapidly in the last decade while coal consumption has continued to grow. There has been a very clear decoupling since the mid-2000s. Again, implementing “scrubber” technologies has allowed China to drastically reduce local air pollution while continuing to burn more fossil fuels (increasing its contribution to global climate change).

In India, SO₂ emissions are still growing. While these emissions have grown more slowly than coal consumption in the last decade, they continue to increase. Just 8% of India’s coal plant capacity has desulfurization technologies installed.⁸

India is not alone. Many low-to-middle-income countries are still on the upward part of the trajectory because installing pollution controls increases the cost of coal plants — often by around 10% to 30% — and providing cheap energy is usually a higher short-term priority.⁹ More than half of India’s coal plants have had a “bid awarded” to have desulfurization technologies installed, but increasing costs have led to huge delays.⁸

What’s clear is that emissions can fall very quickly once countries want to turn that corner. China provides one of the most stunning examples of this. Emissions have fallen by three-quarters since their peak in 2006 and by two-thirds in the last decade alone.

I am more optimistic that low-to-middle-income countries can go through this transition much more quickly than the UK or the US because they can learn from the countries that have already done it. In the 1980s and 1990s, Europe and North America had to design commercial-scale technologies that could remove sulfur from coal plants. They had to bring these prices down. They had to design policies and trading systems from scratch. The countries that follow don’t face uncharted territory; they can take advantage of the successes and failures of the front-runners to do it cheaper and faster. Catching up is easier than leading the way.

The reduction in nitrogen oxides (NOx) — one of the most damaging air pollutants to human health

Nitrogen oxides (called “NOx”) are a group of local pollutants that have been a main target for public health experts and policymakers. NOx is also emitted when fossil fuels are burned — from power stations, industry, or transport fuels.

Many countries have successfully reduced NOx emissions over the last few decades. Part of this has come from stricter pollution controls on power plants and industry. But here, I want to focus on reductions from transport, particularly road transport.

Road transport is one of the main sources of NOx, and for the huge number of people living in towns and cities — with high levels of congestion and traffic — it’s the largest source of NOx that they’re exposed to.

In the chart below, you can see the dramatic reduction in NOx emissions from transport in the UK since 1950. It follows a very symmetrical pattern: climbing steeply through to the 1980s before peaking in 1990 and then falling. Emissions within the last few years have dipped lower than 1950 levels.

What explains this?

The steep rise coincided with an increase in the number of miles driven on British roads. From 1952 to 1990, the number of miles driven by cars, buses, trucks and motorcycles increased about 300%.

You can see this in the chart below, which shows the relative change in road mileage (in blue) and NOx emissions from transport (in red) in the UK since 1952.¹⁰

NOx emissions from transport were also climbing but faster, for several reasons. First, other transport sectors that emit NOx, such as aviation and rail, were growing. Second, the types and sizes of vehicles being driven on the roads were changing, too.

However, NOx emissions peaked in 1990 and have fallen steeply while the number of miles driven has continued to increase. Brits have driven more but emitted much less.

How was this possible? Why did NOx emissions decline so steeply over the last three decades?

Emissions limits for cars and technological advancements from automakers have made our cars much less polluting than they were 30 years ago.

In 1992, the first “Euro” standards for vehicles were put into force. These standards — which applied to all countries in the European Union, plus Norway, Iceland, and Liechtenstein — were designed to reduce emissions of harmful local air pollutants, including NOx.¹¹ All new vehicles sold in these countries had to be below these emission limits, and these standards were tightened over time. “Euro 1” was launched in 1992, and we’re now on Euro 6 standards.¹²

This means that the cars on our roads have become steadily “cleaner” over time.

To comply with regulations, car manufacturers have had to innovate on technologies that can reduce the emissions of NOx and other pollutants from car exhausts. These technologies have included catalytic converters, filters for particulate matter, gas recirculation — which lowers the temperature of combustion and therefore produces less NOx from the exhaust — and “lean NOx traps” — which convert NOx into other less harmful nitrogen gases.

These have been extremely successful in reducing levels of harmful pollution in many cities.

The chart below shows the reduction in NOx emitted per kilometer by diesel and petrol cars in the UK since 1998. Diesel cars are still worse for local air pollution than similar petrol models, but both fuel types emit less than 15% of what they did in the late 1990s.

Download image

As you can see in the next chart, low-to-middle-income countries are much further behind in this emissions curve. But some middle-income countries have passed their peak, including China, South Africa, and Brazil. And emissions growth is slowing down in lower-middle-income countries like India, Bangladesh, and Rwanda.

This is similar to the patterns that we saw for SO₂ earlier.

Lower-income countries should be able to experience a faster and shallower emissions curve. Many have adopted similar regulations to the “Euro” standards, and the use of technologies such as catalytic converters and NOx traps in exhausts has been established for a long time. These technologies have become mainstream for manufacturers, not just in Europe or North America but across most markets.

Electric transport is another huge innovation that should allow many countries to scale up road transport without NOx emissions. Electric vehicles produce no tailpipe emissions, eliminating NOx entirely. They were once considered a luxury product due to their high cost, but battery prices have fallen rapidly. As a result, many EVs now cost about the same as petrol cars and are cheaper to operate. This means they could soon be the most affordable option for consumers in developing markets.

Electric motorcycles, which are being adopted across many lower- and middle-income countries, are also having a big impact on city pollution. Rwanda’s capital, Kigali, has already banned the registration of new gasoline motorcycles, accelerating the move to all-electric ones.

International collaboration and lesson-sharing can save many lives from air pollution

The point of highlighting these successes in reducing air pollution is not to make us complacent. It’s to show what can be done and help us understand what technologies and policy decisions can and can’t be replicated elsewhere. Seeing what is possible should make us more ambitious.

Low- and middle-income countries have the opportunity to follow a much cleaner development pathway than the UK or the US. They can increase energy use and improve living standards with a fraction of the environmental impact. But they can’t and won’t be able to do that if they ignore the innovations that made a difference.

We’re already seeing these cleaner pathways. Compare today's per capita sulfur dioxide emissions in India and China to the UK's trend over the past few centuries. You can see this in the chart below. China peaked at around one-fifth of the levels of the UK. And while India’s emissions are still rising, they’re a fraction of what the UK’s used to be. By implementing the best lessons from those that have gone before them, they can certainly peak at far lower levels.

This really matters. Billions of people are exposed to dangerous levels of air pollution. By accelerating the transition to cleaner energy technologies, we can save millions of lives every year.¹³

Continue reading on Our World in Data

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This data review presents published estimates of the global death toll from air pollution and provides the context that makes them understandable.

Air pollution: does it get worse before it gets better?

Air pollution tends to get worse as incomes rise, then it turns and pollution levels decline.

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Hannah Ritchie (2025) - “In many countries, people breathe the cleanest air in centuries. What can the rest of the world learn from this?” Published online at OurWorldinData.org. Retrieved from: 'https://ourworldindata.org/cleanest-air-lessons' [Online Resource]

@article{owid-cleanest-air-lessons,
    author = {Hannah Ritchie},
    title = {In many countries, people breathe the cleanest air in centuries. What can the rest of the world learn from this?},
    journal = {Our World in Data},
    year = {2025},
    note = {https://ourworldindata.org/cleanest-air-lessons}
}

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