Millions of people across the US and Canada experienced some of the worst air quality in the world last week as smoke from Canadian wildfires blanketed towns and cities with thick, orange smog.
In New York, residents were urged to stay inside their homes and wear high-grade face masks when heading outside.
It has been common knowledge for some time that exposure to severe air pollution is harmful to health, particularly for people with existing respiratory conditions. But what is becoming increasingly clear from recent research is that poor air quality isn’t just a problem for the lungs. Pollution particles – whether from wildfire smoke, car exhausts, truck tyres or plastic waste – can cause damage throughout the body.
Here’s what we know from the latest science on air pollution and health.
Air pollution affects the whole body – not just the lungs
Poor air quality has long been linked to respiratory conditions such as asthma and reduced lung function. But research in recent years has demonstrated that the damage caused by a specific kind of pollution – fine particulate matter – can be carried throughout the body.
“If particles in the air are small enough, they can enter deep into the lungs, and there they are deposited in the air sacs,” says Annette Peters at Helmholtz University Munich, Germany.
Such deposits trigger activity by macrophages, a type of white blood cell that removes bacteria and other microorganisms from the body. These macrophages recruit other immune cells from elsewhere in the body, causing inflammation and damaging cells in the process. “There is a systemic signal which then helps clean up the lungs, but also transmits the potential negative effects of the air pollution to the entire body,” says Peters.
We are still learning how harmful airborne plastic is
Airborne microplastics form part of the particulate matter pollution that damages human health, but little is known about the specific impact of plastic particles on the human body. Most of the research comes from laboratory experiments on cells, or on mice, says Stephanie Wright at Imperial College London, and these studies rely on commercially available polystyrene spheres to act as microplastic samples. “We don’t know how that would extrapolate to the types of microplastic we know are in air,” she says.
There is some suggestion that particle shape may play an important role. Strands of fibres, for example, may prove harder for macrophages to clear up, causing greater inflammation in the body. But more work is needed to understand what kind of plastic particles, including fibres, are in the air around us before we can understand the scale of the threat they pose. “If you want to understand the level of risk, you need both exposure and hazard data,” says Wright.
Air pollution can worsen hay fever and allergies
Life in the city can make summertime sneezing fits worse, with recent research suggesting that air pollution exacerbates hay fever and other allergies.
A recent study assessed 36,145 symptom reports submitted by people in the UK with hay fever between 2016 and 2020. It found that people living in urban areas experienced hay fever symptoms such as runny nose, sore eyes and wheezy breathing that were roughly twice as severe as those in rural areas.
People in urban areas were also more likely to experience worse symptoms when ozone levels were high, the researchers found. Ground-level ozone pollution is formed when sunlight interacts with hydrocarbons such as methane and nitrogen oxides, which are emitted from vehicle engines.
Meanwhile exposure to air pollution – particularly early on in life – has been linked to the development of other allergies. A US study found that exposure to isocyanate, a chemical found in wildfire smoke and vehicle exhaust fumes, can alter skin bacteria, causing eczema.
Another study, this time of 2598 preschool children in China, found that the development of food allergies was associated with exposure to both indoor and outdoor air pollution. “Our study indicates that, in addition to gut and skin, airway may be a new route of food sensitization,” the researchers concluded.
Heatwaves make air pollution more dangerous
One emerging area of research is the link between climate change and air pollution. Recent studies suggest that the mortality rate during a heatwave jumps when the high temperature is combined with poor air quality. According to a European Union research project, extreme heat – defined according to the normal range for each city – results in a 0.4 per cent increase in mortality when pollution levels are low. At medium pollution levels, there is a 2.6 per cent rise in mortality, and with high pollution levels, there is an 8 per cent increase in mortality.
Researchers believe there could be two possible causes for this. “One is that the heat and sunshine themselves alter the mix of air pollution,” says Klea Katsouyanni at Imperial College London. “That is associated with higher ozone levels and then some higher levels of secondary particles.” It may be that these pollutants are more toxic to human health. The other possible explanation is perhaps more straightforward: “It may be that, during hot periods, people spend more time outside and they get more exposed to pollution,” she says.
When it comes to exposure risk, occupation matters as much as address
More deprived neighbourhoods tend to have poorer air quality, while richer, leafier areas have quieter, cleaner streets.
But that trend doesn’t always hold true, according to Ben Barratt at Imperial College London. “Some of the classiest postcodes in London have got high pollution levels,” he pointed out during a conference in London last week. Some affluent areas of west London suffer poor air quality because they are near busy, urban thoroughfares, he said.
Just as important as your residential address is your occupation. During a three-year study in London, six individuals from the same area of the city, but with different occupations, carried personal air quality monitors to track their exposure to black carbon – tiny particles of soot – throughout the day.
“What we found was a huge difference between those who are exposed to the lowest levels of pollution and those exposed to the highest,” Barratt told the conference. “What really stood out was the office worker who was working in central London – the most polluted part of the UK – had the lowest exposure because he was working in a mechanically ventilated office for most of the day. And the ambulance driver had the highest exposure, 2.5 times higher [than the office worker].”