Air pollution is one of the most significant health threats in the world. In Sweden, air quality is improving, but in other parts of the world, the trend is going in the wrong direction. At the same time, research shows that even very low levels of pollution, below legal limits, harm our health.
Text: Annika Lund, first published in Medicinsk Vetenskap nr 2 2025
In December 2020, a historic ruling was made by a British court. It determined that air pollution had caused the fatal outcome of an asthma attack in a nine-year-old girl. She lived in south London, near a heavily trafficked ring road, and had her school was in the same area. It was only after her death that her mother realised that poor air quality was relevant to the case. She took it to court, where it was found that air pollution in the girl's neighbourhood had significantly exceeded legal limits. In the death certificate prepared for the court, air pollution was listed as the cause of death. The girl is believed to be the first person ever to have poor air quality officially recorded as a cause of death. The court awarded damages to the mother.
Causes millions of deaths
But regardless of what death certificates say around the world, air pollution is a major health issue. Globally, it is estimated to cause around 4.2 million deaths per year, mainly through acute heart and lung problems, according to the World Health Organisation (WHO). Within the EU, it is estimated to cause around 300,000 deaths annually. The corresponding figure for Sweden is 6,700 deaths per year.
"The court case in London brought poor air quality into the spotlight as a health issue. Air pollution is easy to ignore in our part of the world because most people do not notice it, unlike in other parts of the world," says Petter Ljungman, cardiologist and researcher at the Institute of Environmental Medicine at Karolinska Institutet.
In autumn 2024, a new EU directive on air quality was adopted, coming into force in December 2026. By then, all member states must aim for new, lower limit values, which must be met by 2030.
The rules are strict for countries that fail to meet the targets. A new feature of the directive is that each member state must make it easier for individuals to claim compensation if their health has been harmed by air pollution, provided the responsible authorities have not done enough to ensure air quality meets legal standards. This part of the directive takes effect as soon as it comes into force in 2026. Another requirement is to make it easy for EU citizens to find out how clean the air is.
So how is Sweden doing? Are we breathing clean air?
The air is becoming cleaner in Sweden
Petter Ljungman and his colleagues have developed a model to calculate air pollution at a very high-resolution,, down to areas as small as 50 x 50 metres. Using this model, they have mapped pollution levels in six Swedish cities: Gothenburg, Linköping, Lund, Malmö, Stockholm and Umeå. The data covers the years 2000, 2011 and 2018, allowing researchers to track changes in air quality over time.
The model shows that air in Sweden is getting cleaner. This applies to both fine and coarse particles (PM2.5 and PM10) as well as nitrogen dioxide. Of these, the fine particles are particularly harmful for health.
The researchers have calculated how many lives have been saved as a result of cleaner air. POver the entire period, more than 2,700 deaths have been avoided in these cities, home to 5.5 million Swedes.
"The improved d air quality is due to the stricter regulations. And that, in turn, is thanks to strong scientific evidence showing that air pollution costs lives. Long-term advocacy has made a difference," says Petter Ljungman.
At the same time, the study shows there is room for improvement. Air quality was worst in Malmö, where all measured pollutants were highest. The explanation lies in its proximity to the continent - particles can travel long distances, especially the fine ones, which are considered the most harmful. Some of the pollution in Europe consists of desert dust blown all the way from the Sahara. The slightly larger particles fall to the ground more quickly but can also travel far.
The country's second-highest levels of fine particles and nitrogen dioxide are in Stockholm.
The source is largely local traffic, especially diesel vehicles. In Gothenburg, we find the second-highest levels of larger particles which is stirred up by wear from tyres and road surface. Shipping and industry also contribute to air pollution in Gothenburg.
Broadly speaking, air tends to be more polluted in southern Sweden. But even in Umeå, high levels are recorded. There, traffic and wood burning are the main sources.
But by international comparison Sweden has clean air everywhere.
And we are moving towards even cleaner air, just like the rest of Europe. Air quality is also improving in the US and Canada.
The trend in India is heading in the wrong direction
"In other parts of the world, emissions are increasing. In those countries, there is limited research activity to raise awareness about air pollution and its health effects," says Petter Ljungman.
For several years, he has been collaborating with researchers in India. They are calculating pollution levels in India using a different method than the one used in the Swedish study. In India, researchers have combined satellite data and fixed monitoring stations with weather data, demographic information, and land use data. The result is a nationwide map of air pollution, with a resolution of 1 x 1 kilometre, covering each year from 2009 to 2019.
Such detailed knowledge of the country's air quality has previously been lacking.
"Our hope is that other researchers will use this information and build on it for their work, for example by adding more health data," says Petter Ljungman.
The researchers have already taken it further. In a newly published study, they added data on outdoor temperatures. This gave an even bleaker picture of the challenge India faces: the effects of high levels of air pollution are worsened by high temperatures. And both are common in India.
In India, the legal level for PM2.5 is 40 micrograms per cubic metre as an annual average. But out of India's total population of 1.4 billion people, 1.1 billion breathe air with higher pollution levels than that.
And India's limit is already high. The World Health Organisation (WHO) recommends much lower levels: no more than 5 micrograms per cubic metre annually. Nowhere in India meets that standard.
The researchers estimate that 16.6 million people in India died as a result of air pollution during the ten-year period they studied, based on WHO's recommendation.
And unfortunately, the trend in India is heading in the wrong direction. Air quality worsened over the period.
"The disease burden linked to air pollution is huge in India, much greater than the burden of disease linked to smoking," says Petter Ljungman.
The area south of the Himalayas in northern India has the country's worst air quality. The mountain range acts as a barrier that traps particles, soot and gases.. The region has extensive agriculture, and farmers burn crop stubble before replanting. In Delhi, a city of 30 million located in the region, air is further burdened by traffic and industry.
Delhi is one of the most polluted cities in the world. Petter Ljungman and his colleagues calculated an annual average of nearly 120 micrograms per cubic metre, far above WHO's recommended maximum of 5. Levels were even higher during temporary daily peaks.
In India, the entire population breathes more fine particles than WHO recommends. In Sweden, 65 per cent of the population does.
There is no safe level
How important is it to reach the WHO recommendation? Do the EU's new limit values-which Sweden must meet by 2030-go far enough? What is actually a safe level?
"There is no safe lower limit. Medically speaking, the limit should be zero. WHO has factored in technical and economic considerations and set a value that is considered more realistic to aim for," says Petter Ljungman.
No safe threshold for air pollution - study confirms
This has been confirmed, among other sources, by the ELAPSE study, which included nearly 140,000 people from four different European countries.. Some lived in areas with relatively clean air, below WHO's recommended level. The study participants were followed for 17 years.
The study showed that long-term exposure, even to low levels of air pollution, increases the risk of stroke, cardiovascular disease, other serious illnesses and leads to a higher mortality.
According to a UN report published in 2023, nine out of ten people globally live where air pollution levels exceed WHO recommendations. And this has major consequences for global health. Fine particles (PM2.5) alone reduce global life expectancy by about as much as smoking, according to the report. Far more than alcohol consumption and unclean water.
Bad for the heart, blood vessels and lungs
On the platform 'Our World in Data', the burden of disease caused by various risk factors is compared. Air pollution tops the list. In second place is high blood pressure, followed by smoking and obesity.
Poor air quality increases the risk of asthma, worsens existing asthma, impairs lung function, and contributes to respiratory infections, pneumonia and lung cancer.
However, cardiovascular diseases account for the largest share of the health burden from air pollution. According to the summary of the Swedish Environmental Protection Agency's 2023 report 'Air & Environment' , air pollution increases the risk of the following conditions: high blood pressure, blood clots, heart rhythm disorders (arrhythmias), heart failure, heart attack, cardiac arrest and stroke.
According to cardiologist Petter Ljungman, there are several theories about how poor air quality causes cardiovascular disease. The most widely accepted is that the pollutants cause local inflammation in the lungs. Substances from the immune system then enter the bloodstream and trigger widespread, low-grade inflammation in the blood vessels. Less well-established is the idea that air pollution may affect heart rhythm and blood vessel constriction via the autonomic nervous system, the part of the nervous system that operates involuntarily. This effect may also begin locally in the lungs.
It is known that the fine particles can pass into the bloodstream via the alveoli in the lungs. They can also travel to organs such as the liver or brain.
In addition to heart and lung disease, poor air quality increases the risk of diabetes, dementia, premature birth and pregnancy complications.
"More and more studies are showing how air pollution increases the risk of various chronic diseases and cancer. Inflammatory processes are a common denominator," says Petter Ljungman.
Some people are more sensitive to air pollution, especially those who already have heart or lung conditions, and older adults.
Children are particularly sensitive
Children are a particularly vulnerable group. Epidemiologist Olena Gruzieva , who leads a research group at the Institute of Environmental Medicine at Karolinska Institutet, lists several reasons why. Children spend a lot of time outdoors and are active, so they tend to breathe more intensively and take in more air per kilogram of body weight. They also have narrower airways than adults. In addition, their immune systems are immature, which contributes to their sensitivity.
Pregnant women are also particularly vulnerable to poor air. The risk of preeclampsia increases, as does the risk of low birth weight.
"We must aim for even lower levels of air pollution. The levels we have now are not low enough to protect our entire population," says Olena Gruzieva.
She and her colleagues studied lung function of 177 infants, all healthy and born full term. They lived across central Stockholm at addresses where the researchers could calculate levels of particles and nitrogen dioxide. Half lived on streets with relatively poor air quality, worse than WHO's recommendations. Yet, in an international comparison, the air quality was still considered good. The average pollution levels were below both current Swedish legal limits and the stricter limits that will apply from 2030.
The children were examined using plethysmography, a method in which breathing is measured via a vest that wraps around the chest, sometimes with slight resistance. It measures, among other things, how much air can be exhaled during the first half-second, an key parameter for assessing airway obstruction, i.e. resistance in the airways.
Infants living on polluted streets had poorer lung function, already at six months old.
"We know this can have long-term effects. If you have reduced lung function already in infancy, it will be difficult to reach expected lung capacity later in life," says Olena Gruzieva.
Poor lung function early in life is associated with an increased risk of developing several diseases later on, such as asthma, COPD and cardiovascular disease.
The researchers have studied the long-term effects of air pollution in a Swedish context by following over 4,000 children in what is called the BAMSE study. The children were born in the mid-1990s and grew up in Stockholm. They lung function was measured at ages 4, 8, 16 and 24. In this study too, the researchers calculated air pollution levels at the children's home addresses down to street level.
Children exposed to poorer air quality during their first year of life had reduced lung function in school age. The effect on the lung function persisted into adolescence and up to young adulthood. It also appeared that early-life exposure to air pollution increased the risk of childhood asthma and chronic mucus cough in young adulthood. The researchers therefore believe that the earliest period of life is particularly critical when it comes to air pollution exposure.
The children in the BAMSE study are now in their 30s and the researchers plan to continue following them.
- Type 2 diabetes, cardiovascular disease, and many other diseases take a long time to develop. The study'sparticipants are still too young for us to confirm such effects," says Olena Gruzieva.
Increases the risk of dementia
Research on older adults shows that poor air quality can have very long-term effects. And organs ther than the heart, blood vessels and lungs can be affected. Air pollution may have neurotoxic effects and, over time, increase the risk of dementia. This is the result of research by Debora Rizzuto , who leads a research group at the Aging Research Center (ARC) at the Department of Neurobiology, Care Sciences and Society.
In one study, she followed more than 2,500 people living on Kungsholmen in Stockholm. They were on average 73 years old when the study began, and all were healthy at that point. During the study, 376 of them were diagnosed with dementia.
Using their addresses, researchers could determine how much air pollution each of the study participants had been exposed to. The average level of fine particles for the whole group was 8.3 micrograms per cubic metre, which is more than WHO's recommendation, but below EU's legal limits.
At the individual level, the air quality that study participants were exposed to varied. Even small differences had a significant impact on the development of dementia. Each additional microgram per cubic metre of fine particles increased the risk by 70 per cent.
"Air pollution is a modifiable factor that increases the risk of dementia," says Debora Rizzuto.
The greater the improvement in air quality, the greater the health benefits
A key finding from the BAMSE study is that improvements in air quality matters. Since the children were born in the 1990s, air quality has gradually improved across Stockholm. Cars and fuels have evolved, congestion charges and environmental zones have been introduced, and stricter requirements have been imposed in public procurement.
In some areas, improvements were greater, for example, where studded tyre bans were introduced. The researchers examined how much air quality improved for each child during their first eight years of life. They then looked at how many had developed asthma by the age of 24. The result was clear: the greater the improvement in air quality, the greater the health benefit. Children who experience cleaner air had an 11 per cent lower risk of developing asthma than those who lived with unchanged air quality.
A reason to be hopeful, say the researchers.
Improved public health is the objective of the City of Stockholm's decision to introduce an environmental zone class 3, a 'zero emission zone', in a central area of the city. The regulation entails a ban on petrol and diesel vehicles. The area is small but very busy and includes an entrance and exit to the heavily trafficked Klara tunnel.
Ahead of the decision, Olena Gruzieva submitted a consultation response, in which she described, among other things, the results of her own studies.
In May 2024, the City of Stockholm voted in favour of introducing the class 3 environmental zone starting on 31 December the same year. According to the city's own impact assessment, it is likely the first of its kind in all of Europe.
However, several parties have appealed the decision, including business owners concerned that customers and deliveries will have difficulty accessing the area. These legal proceedings are still ongoing, so the strict environmental zone regulation has yet to be implemented.
"We are doing what we can to communicate the results of our studies. My impression is that we are met with understanding from political decision-makers," says Olena Gruzieva.
