Why is clean air important?
We breathe thousands of times every day. The air entering our lungs can contain gases, tiny particles, smoke, dust and other substances.
Air pollution can affect the lungs, heart, brain and other parts of the body. It is linked with diseases including asthma, chronic obstructive pulmonary disease, stroke, heart disease and lung cancer.
Air pollution is not only an individual problem. The quality of the air around us is influenced by transportation, energy production, industry, agriculture, household fuels, waste, fires and the way communities are planned.
If everyone needs air to live, should clean air be considered a shared public-health responsibility?
Personal hints
Look around you
- What kinds of air do you breathe at home, at school and outdoors?
- Can you identify places where smoke, traffic or dust may be greater?
- Have you ever noticed an air-quality warning?
- Where could you find reliable information about air quality?
Look beyond yourself
Not everyone has the same control over the air they breathe.
A child living near a busy road, a family using polluting cooking fuels, or a worker exposed to dust may face risks that cannot be solved simply by telling the person to "make healthier choices."
Explore
Let's learn the language scientists and public-health professionals use to describe air pollution.
Air pollution
Air pollution means that harmful chemical, physical or biological substances are present in indoor or outdoor air.
Indoor air pollution
Pollution inside homes, schools, workplaces and other buildings.
Outdoor air pollution
Pollution in the air around us, often influenced by traffic, industry, energy production, fires and other sources.
PM₂.₅
Very tiny particles that are 2.5 micrometres or smaller in diameter.
PM₁₀
Particles that are 10 micrometres or smaller in diameter.
Ozone (O₃)
A gas that can be harmful to breathe when it forms near the ground. It is different from the protective ozone layer high in the atmosphere.
Nitrogen dioxide (NO₂)
A gas commonly associated with burning fuels, including emissions from vehicles and other combustion sources.
Carbon monoxide (CO)
A colourless and odourless gas produced when fuels do not burn completely.
Sulfur dioxide (SO₂)
A gas released mainly by burning sulfur-containing fuels and some industrial processes.
Learn
Indoor and outdoor pollution
Air pollution can be found both inside and outside buildings.
Indoor sources can include smoke from cooking or heating with polluting fuels, tobacco smoke, some chemicals, dust, mould and poor ventilation.
Outdoor sources can include traffic, industry, power generation, construction, agriculture, waste burning and wildfire smoke.
Why are tiny particles important?
Some particles in polluted air are so small that we cannot see them.
PM₁₀ includes particles up to 10 micrometres across. PM₂.₅ includes even smaller particles, up to 2.5 micrometres across.
The smaller size of PM₂.₅ allows these particles to travel deep into the lungs. Fine particulate pollution is therefore an important public-health concern.
A micrometre is one millionth of a metre. A human hair is much wider than a PM₂.₅ particle. That is why these particles are often invisible.
Air pollution and health
Air pollution can affect people throughout life. Children, pregnant people, older adults and people living with chronic diseases may be particularly vulnerable to some effects.
Health effects can include respiratory symptoms, asthma exacerbations, cardiovascular disease, stroke, chronic respiratory disease and cancers.
The health impact depends on the pollutant, concentration, duration of exposure, individual susceptibility and the surrounding social and environmental conditions.
Household air pollution
In many parts of the world, families still cook or heat their homes using fuels and technologies that produce large amounts of smoke.
WHO reports that around 2.1 billion people were still cooking with open fires or inefficient stoves using fuels such as wood, charcoal, crop waste, dung, coal or kerosene in 2025.
This is not simply a question of personal choice. Access to affordable clean energy, infrastructure, income and public policy all matter.
Wildfire smoke
Wildfires can produce smoke containing particulate matter and other pollutants. Smoke can travel long distances, meaning that communities far from the fire may also experience poor air quality.
Wildfire smoke also shows why climate, environment, emergency preparedness and health cannot be treated as completely separate subjects.
Clean air is a systems issue
Air quality is influenced by choices made by households, businesses, cities and governments.
Cleaner transportation, cleaner energy, better urban planning, safer industrial processes, improved household energy and effective regulation can all contribute to healthier air.
How is air pollution measured?
Scientists use instruments to find out what is in the air and how much of it is present.
Concentration
Scientists measure how much of a pollutant is present in a certain amount of air.
µg/m³
This means micrograms per cubic metre.
In simple words: it tells us how much pollution is found in a particular volume of air.
Monitoring stations
Special instruments can continuously or regularly measure pollutants at selected locations.
Air Quality Index
Some governments combine pollution measurements into an easier-to-understand air-quality scale.
The exact scale and categories can differ between countries and jurisdictions.
What does PM₂.₅ = 20 µg/m³ mean?
It means that the measured air contains an average concentration of about 20 micrograms of PM₂.₅ in each cubic metre of air during the specified measurement period.
The number is not a percentage and it does not mean that every breath contains exactly the same amount. Air pollution changes over time and from place to place.
Why do measurements matter?
Measurements help scientists understand exposure, help health authorities identify pollution problems, and help governments evaluate whether policies are improving air quality.
If one neighbourhood has more pollution than another, what information would you want before deciding why?
Think
Critical-thinking questions
- Why might air pollution be higher near a major road than in a low-traffic area?
- Why can indoor air pollution be a serious problem even when outdoor air looks clean?
- Why might PM₂.₅ be difficult to see but still important for health?
- If two communities have different pollution levels, what social and economic factors might help explain the difference?
- Who should be responsible for reducing air pollution: individuals, businesses, cities, governments—or all of them?
- Why might a country need both air-quality monitoring and strong environmental regulations?
Connect: From Self to World
My air
Notice the air around you and learn how pollution can affect health.
Our indoor air
Think about ventilation, smoke, cooking, heating and other indoor sources.
Our neighbourhood
Explore traffic, industry, construction, green space, wildfire smoke and local air-quality monitoring.
Policies and systems
Ask how governments regulate emissions, monitor air quality and support clean energy.
One atmosphere
Air pollution crosses borders and connects health, climate, energy, development and equity.
Social Determinants of Health
The air people breathe is shaped by the conditions in which they live, learn, work and travel.
- Income: influences housing, energy choices, transportation and exposure to environmental risks.
- Housing: affects ventilation, dampness, mould, heating and indoor pollution.
- Location: some communities may be closer to major roads, industrial facilities or other pollution sources.
- Energy access: access to affordable clean household energy can reduce household air pollution.
- Work: some occupations involve exposure to dust, fumes or other pollutants.
- Urban planning: transport systems, housing and land use can influence population exposure.
- Healthcare access: pollution-related illness may be harder to prevent or treat where healthcare is difficult to access.
Is it fair to tell everyone to "avoid polluted air" when some people have much less control over where they live, work or travel?
Sustainable Development Goals
Air pollution demonstrates why the SDGs are interconnected. Health depends not only on medical care but also on energy systems, cities, transport, inequality, production and climate.
Global Leadership & Evidence
Who helps understand and reduce air pollution?
- WHO — develops health-based air-quality guidelines, synthesizes evidence and supports countries on health and air pollution.
- UN Environment Programme (UNEP) — works on environmental policy and global environmental action.
- National and provincial/state authorities — monitor air quality, regulate emissions and implement public-health measures.
- Local governments — influence transportation, land use, waste management, urban planning and local environments.
- Universities and scientific institutions — measure pollution, study health effects and develop new methods and technologies.
- Communities and civil society — can monitor local concerns, advocate for healthier environments and participate in environmental decision-making.
Global Evidence Date
Global evidence: WHO, 2026
Key global air-quality guideline: WHO, 2021
GHE last reviewed: August 2026
Next scheduled review: August 2027
Air-pollution evidence continues to develop. GHE therefore treats this module as living evidence, not a static textbook.
Reflect
My reflection
What did you learn about air pollution that you did not know before?
Which pollutant or source would you like to understand better?
Equity reflection
Which groups may have less control over the air they breathe?
What could governments and communities do to reduce these inequalities?
Global reflection
Why can air pollution not always be solved within the boundaries of one city or country?
Act
- Learn how to find reliable local air-quality information.
- Learn what PM₂.₅ and PM₁₀ mean.
- Discuss why clean indoor air matters at home and at school.
- Learn how transportation and energy choices influence air quality.
- Explore how your community monitors air pollution.
- Ask whether all communities have equal exposure to pollution.
- Support evidence-based policies that create healthier environments.
- Share reliable information rather than unverified claims about air pollution.
Explore Further
Want to go deeper? Start with authoritative sources and then explore the evidence behind the science.
WHO — Air Pollution
An overview of indoor and outdoor air pollution, major pollutants, sources and health effects.
Explore WHO →WHO Global Air Quality Guidelines
The international health-based reference for PM₂.₅, PM₁₀, ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide.
Read the guidelines →WHO — Household Air Pollution
Learn why cooking and heating fuels can affect household air quality and health.
Explore household air pollution →WHO — Air Pollution & Health
Explore WHO guidance connecting air pollution, environmental conditions and health.
Explore the guidance →WHO — Health Effects of Air Pollution
A recent WHO evidence brief on the health effects of air pollution across multiple body systems.
Explore the evidence →Think about children
Ask why children may be especially important when communities make decisions about air quality, transport, schools and urban planning.
Start exploring →Test Your Thinking: 10 MCQs
These questions test knowledge, interpretation, application, measurement, SDH, SDGs and global-health thinking.
1. What is air pollution?
Answer: B
2. What does PM₂.₅ describe?
Answer: A
3. Why is PM₂.₅ particularly important for health?
Answer: B
4. What does µg/m³ tell us?
Answer: B
5. Which is an example of household air pollution?
Answer: A
6. A neighbourhood near a busy highway has higher pollution than another neighbourhood. What is the best public-health question?
Answer: B
7. Which SDG is most directly connected to reducing the health effects of air pollution?
Answer: A
8. Why can cleaner household energy improve health?
Answer: A
9. Which statement best reflects health equity?
Answer: B
10. Which response best represents the GHE approach to air pollution?
Answer: B