Key figures
- 99% of the world’s population breathes air exceeding WHO guideline limits
- Outdoor and household air pollution are linked to millions of premature deaths each year
- About 2 billion people still cook with polluting fuels and technologies
- China cut fine-particle pollution by roughly 40% in under a decade
Air pollution rarely makes headlines the way floods and wildfires do. It is invisible most of the time, and its victims do not die in a single dramatic event but gradually, from strokes, heart attacks, lung cancer and respiratory infections. Yet it is one of the largest environmental threats to human health in the world. According to the World Health Organization (WHO), 99% of the global population lives in places where air quality exceeds its guideline limits. Together, outdoor and household air pollution are associated with several million premature deaths every year — more than malaria, tuberculosis and HIV combined.
The challenge: what we breathe
The most dangerous pollutant is fine particulate matter, known as PM2.5 — particles less than 2.5 micrometres across, about one-thirtieth the width of a human hair. They are small enough to penetrate deep into the lungs and pass into the bloodstream, where they cause inflammation that damages the heart, blood vessels and brain. Research has linked long-term exposure to fine particles not only to heart and lung disease, but also to diabetes, low birth weight and dementia.
Fine particles come from many sources: vehicle exhaust, especially from diesel engines; coal-fired power plants; heavy industry; the burning of crop residues and household waste; construction dust; and, increasingly, wildfire smoke. Other harmful pollutants include nitrogen dioxide, produced mainly by road traffic, and ground-level ozone, which forms on hot, sunny days when pollutants react in sunlight. As the climate warms, both wildfire smoke and ozone are becoming more common.
Canadians know this first-hand. During the extreme fire seasons of 2023 and 2025, smoke pushed air quality in cities such as Montreal and Toronto to some of the worst levels in the world for days at a time. The 2026 season again brought smoke warnings to communities far from the fires.
Indoors, the problem is even more personal. Around two billion people, mostly in sub-Saharan Africa and Asia, still cook with wood, charcoal, crop waste, dung or kerosene on open fires or simple stoves. In poorly ventilated homes, the smoke can reach levels many times higher than the worst outdoor pollution. Women and children, who spend the most time near the fire, bear the heaviest burden. Collecting firewood also takes hours each day and contributes to deforestation.
The burden is unequal within countries as well. Low-income neighbourhoods are often located next to highways, ports and industrial zones, exposing residents to more pollution while they have less access to health care.
A problem linked to climate
Air pollution and climate change share many of the same causes. Burning coal, oil, gas and biomass releases both carbon dioxide and harmful pollutants. Some pollutants, such as black carbon (soot) and methane, which contributes to ozone formation, also directly warm the planet. Black carbon that settles on snow and glaciers darkens their surface, causing them to absorb more sunlight and melt faster. This means that many climate solutions are also air quality solutions — and vice versa.
What can be done
Air pollution is one of the few environmental challenges where rapid, measurable improvements have been achieved within a few years. History offers encouraging examples. In the 1950s, London’s deadly smogs led to the Clean Air Act. In North America, regulations since the 1970s have dramatically reduced sulphur dioxide, lead and fine particles, even as economies grew.
More recently, China’s national action plan on air pollution, launched in 2013 after severe smog episodes in Beijing and other cities, closed or cleaned up coal-fired plants and factories, replaced coal heating with gas and electricity in millions of homes, and tightened vehicle and fuel standards. According to the Air Quality Life Index developed at the University of Chicago, particulate pollution in China fell by roughly 40% in less than a decade, adding measurable time to average life expectancy.
Cities around the world are applying similar approaches. Low-emission zones restrict the most polluting vehicles from city centres; London’s ultra-low emission zone has contributed to significant reductions in nitrogen dioxide. Electric buses, expanded public transit, and safe networks for cycling and walking reduce traffic pollution while also cutting congestion and noise. Paris has transformed major roads into bike lanes, and Bogotá has built one of the largest bus rapid transit and cycling networks in the world.
Cleaning up power generation delivers large benefits. Replacing coal-fired plants with solar, wind and other clean sources removes a major source of fine particles, sulphur dioxide and mercury. Several countries, including Canada, have committed to phasing out conventional coal power, and Ontario’s coal phase-out, completed in 2014, is widely credited with ending the province’s smog days.
Clean cooking is one of the most powerful opportunities for improving health in developing countries. Replacing traditional stoves with liquefied petroleum gas, electric induction cookers, biogas or efficient biomass stoves reduces indoor smoke, saves time spent collecting fuel and protects forests. International initiatives are working to make clean cooking affordable, and the rapid spread of solar home systems and mini-grids makes electric cooking increasingly practical.
Agriculture matters too. In northern India, the burning of rice straw after harvest contributes to severe smog each autumn. Machines that incorporate straw into the soil, and markets that turn crop residues into fuel or building materials, can reduce this burning. Reducing ammonia emissions from fertilisers and livestock also cuts the formation of fine particles.
Monitoring helps drive action. Low-cost air quality sensors now allow communities, schools, journalists and researchers to measure pollution street by street, revealing hotspots that official stations miss. Public data puts pressure on authorities and helps people protect themselves on bad days — for example, by limiting outdoor exercise or using air purifiers.
What you can do
Individuals can reduce their exposure and their contribution to pollution. Walking, cycling or taking public transit instead of driving, avoiding idling engines, choosing electric or efficient vehicles, and avoiding the burning of leaves and household waste all help. At home, good ventilation while cooking, a portable air cleaner with a HEPA filter during smoke episodes, and checking daily air quality forecasts can protect vulnerable family members.
Clean air is a right, not a luxury. Every coal plant replaced by solar or wind, every diesel truck replaced by a clean vehicle and every smoky stove replaced by a clean one reduces both carbon emissions and the pollution that fills hospital beds. Clean air, in other words, is one of the most immediate and tangible rewards of climate action.
Sources
World Health Organization, ambient and household air quality fact sheets; International Energy Agency, clean cooking analysis; Air Quality Life Index (Energy Policy Institute at the University of Chicago); Government of Ontario, coal phase-out reports.
