Indoor Air Pollution: What’s in the Air We Breathe at Home?

We spend much of our lives indoors, at home, at school, at work and in public buildings. Yet the air around us can contain pollutants we cannot see or smell. Cooking, heating, cleaning products, building materials and even moisture can affect the air we breathe. Indoor air pollution comes from many sources, and the best way to deal with it depends on what is present and where it comes from.

The good news is that a few sensible habits can reduce many common indoor pollutants. Other concerns, such as radon or asbestos, need more specific attention.

Where does indoor air pollution come from?

Think of a room as a small environment. Pollutants can enter from outdoors, be released by things inside the building or form through everyday activities. Ventilation helps exchange indoor air with outdoor air, but its benefits depend on the quality of the incoming air and the pollutant involved.

Pollution from aerosol spray

This table is a starting point, not a diagnosis. The presence of a possible source does not automatically mean a harmful exposure to indoor air pollution is occurring.

The type of pollutant, its concentration and how long people are exposed all matter.

How can indoor pollutants affect health?

Different pollutants have different effects. Smoke and fine particles can irritate the respiratory system and contribute to heart and lung problems. Nitrogen dioxide can irritate airways and worsen asthma. Carbon monoxide is especially dangerous because it interferes with the blood’s ability to carry oxygen and can cause serious poisoning.

Household sources of air contaminants

Other concerns develop over longer periods. Radon exposure increases the risk of lung cancer. Lead can harm the developing brain and nervous system, particularly in children. Exposure to asbestos fibres can cause serious diseases, including lung cancer and mesothelioma.

Mold and damp buildings are associated with respiratory symptoms, allergies and asthma-related effects. Cleaning products and other VOC sources vary widely: some cause irritation, while the health effects of others depend on the particular chemical and the amount inhaled.

The key is to avoid treating every indoor contaminant as equally dangerous. A lingering fragrance, visible mold, carbon monoxide and radon are very different problems and call for different responses.

What can you do to improve indoor air quality?

Start with practical steps that reduce pollution at its source.

• Keep smoke out of indoor spaces. Tobacco smoke and smoke from other combustion sources can release harmful gases and particles.
• Ventilate sensibly. Use an externally vented range hood when cooking and provide appropriate ventilation when using paints or cleaning products. Consider outdoor pollution and wildfire smoke before opening windows.
• Maintain heating and cooking equipment. Follow the manufacturer's instructions and arrange qualified service when needed. Install working carbon monoxide alarms as recommended by local safety guidance.
• Control moisture. Repair leaks, dry wet materials and investigate persistent dampness. Cleaning visible mold without fixing the moisture problem may only provide temporary relief.
• Take care during renovations. Older homes may contain lead-based paint or asbestos-containing materials. Avoid disturbing suspect materials until their risks have been assessed.
• Choose products thoughtfully. Use household chemicals according to their labels, avoid unnecessary sprays and fragrances and store products safely.
• Use filtration where appropriate. A suitable air cleaner can reduce certain airborne particles. It will not solve every air-quality problem or replace source control and adequate ventilation.

More ventilation is not always better. During wildfire smoke events or periods of poor outdoor air quality, bringing in large amounts of unfiltered outdoor air may worsen indoor air pollution conditions. The best approach depends on the building, the pollutant and the situation.

Two special cases: radon and carbon monoxide

Radon: a hazard you cannot detect with your senses

Radon is a radioactive gas that forms naturally in soil and rock. It can enter buildings through openings in foundations and accumulate indoors. You cannot reliably detect it by smell, sight or ordinary household air-quality monitors.

Radiation glow

Health Canada recommends testing homes with a long-term test lasting at least three months. Canada's radon guideline is 200 becquerels per cubic metre (Bq/m³). If the test result exceeds that level, consult a qualified radon mitigation professional about reducing the concentration. Sealing visible cracks or opening windows alone cannot establish that a radon problem has been resolved.

Carbon monoxide: an immediate safety concern with regard to indoor air pollution

Carbon monoxide (CO) is colourless and odourless. It can be produced by malfunctioning or improperly vented fuel-burning appliances and by vehicle exhaust. Symptoms of exposure can include headache, dizziness, nausea and confusion. High exposures can be fatal.

Working CO alarms, proper appliance installation and maintenance and safe venting are essential. Never run a vehicle in an attached garage, even with the garage door open. If a CO alarm sounds or you suspect exposure, leave the building and contact emergency services from a safe location.

What about schools, offices, swimming pools and vehicles?

Indoor air quality matters wherever people gather. Classrooms and offices can have problems associated with inadequate ventilation, cleaning products, renovation work, moisture or pollutants entering from outdoors. The appropriate response depends on the suspected source and the building's ventilation system.

Swimming facilities require particular attention to the air above the water. Chlorine-based disinfectants can react with substances brought into the pool by swimmers, forming compounds such as chloramines. Poorly controlled conditions can contribute to eye and respiratory irritation. Pool operators need suitable water treatment, ventilation and maintenance practices.

Concerts and theatrical productions may use fog or haze effects. The health implications depend on the material used, how it is generated, its concentration and the exposure conditions. Anyone responsible for a venue should follow the product instructions and relevant safety requirements rather than assuming that every fog effect is harmless.

Vehicles are another small indoor environment. Exhaust can enter through leaks or other pathways, while particles may enter from outdoor traffic. Keep the vehicle in good repair, avoid idling in enclosed spaces and maintain the cabin air filter according to the manufacturer's recommendations.

Does indoor air need to be tested?

Testing can be useful when there is a specific indoor air pollution question to answer, such as whether a home has elevated radon, whether carbon monoxide may be present or whether a suspected contaminant requires investigation. The test must be suitable for the pollutant and the conditions being assessed.

A low-cost sensor may help track certain conditions, such as particulate matter or carbon dioxide, but it does not measure every pollutant. Carbon dioxide can provide clues about ventilation and occupancy; it is not a universal measure of air quality. A general-purpose air monitor cannot rule out radon, asbestos or lead hazards.

Consider qualified help when a problem persists, when a particular hazard is suspected or when the consequences of a wrong conclusion could be serious. For example, radon testing and mitigation are specialized tasks, while suspected asbestos or lead hazards during renovation call for appropriate assessment and precautions.

Calvin Consulting focuses on outdoor ambient air quality and related environmental assessment services rather than indoor air testing. For indoor concerns, readers should seek a qualified provider whose expertise matches the pollutant and building involved.

Indoor air and the bigger environment

Indoor and outdoor air are connected. Traffic, industrial sources, wildfire smoke and other outdoor emissions can affect the air entering homes and workplaces. Indoor sources can also release pollutants that contribute to broader environmental problems.

Outdoor air-quality professionals use monitoring data, emissions information and dispersion modelling to understand how pollutants move through the atmosphere and where concentrations may be elevated. These methods answer different questions from a home radon test or an investigation of indoor ventilation, but both fields rely on sound measurements, careful interpretation and an understanding of exposure.

Learning how air moves and how pollutants behave is a useful way to connect everyday experience with atmospheric science.

A useful next step

Indoor air pollution can seem mysterious because many pollutants are invisible. Start by identifying possible sources, take sensible steps to control them and seek suitable testing or professional advice when the problem calls for it.

If you know a student, teacher, homeowner or building manager who is curious about the air they breathe, share this page with them. Then explore the related air-quality and meteorology topics to see how the same science connects our homes, our communities and the atmosphere around us.

Search this site for more information now.

Explore more about air quality and the atmosphere

These related topics can help you follow the science further, whether you are a student working on a project, a teacher planning a lesson or a professional looking for a clearer picture of air pollution.

Air Pollution - Explore the main types of pollution, their sources and their effects.

Air Pollution from Vehicles - Learn how exhaust, brake and tire wear and road dust affect air quality.

Air Pollution and Global Warming - Understand the difference between pollutants that affect health and greenhouse gases that influence climate.

Air Quality Modelling - Find out how scientists estimate the movement and concentration of pollutants outdoors.

Air Quality Testers - Explore air-quality measurement and the questions testing can help answer.

What Is the Air Made Of? - Discover the gases that make up our atmosphere and why small amounts of contaminants can matter.

Calm Weather and Inversions - Learn why certain weather conditions can allow pollution to accumulate near the ground.

Measuring Wind Speed and Direction - See how wind measurements help explain the movement of air and pollutants.

Atmosphere Lesson Plans for Teachers - Find ideas for bringing atmospheric science into the classroom.

Science Fair Project Ideas - Explore possible projects about weather, air and the environment.

Meteorology for Kids - Find accessible introductions to the science of the atmosphere.

Ways to Prevent Air Pollution - Consider practical actions that can help reduce pollution.

Do you have concerns about air pollution in your area??

Perhaps modelling air pollution will provide the answers to your question.

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