5 Common Indoor Air Pollutants and their Sources

We tend to think that the indoors are safe than outside. However, the Environmental Protection Agency (EPA) says that the air in homes and other buildings can be more seriously polluted than the outdoor air. Indoor air pollution can cause significant health problems.

People who may be exposed to indoor air pollutants for the most prolonged periods are often those most at risk of the effects of indoor air pollution. This includes children, older adults, and people with long-term (chronic) illnesses. Indoor air quality is affected by pollutants from within and outside an enclosed space. 

Common indoor air pollutants include:

  • Indoor Particulate Matter
  • Carbon Monoxide
  • Volatile Organic Compounds
  • Asbestos
  • Biological Pollutants


1. Indoor Particulate Matter

This graphic depicts size comparisons for particulate matter in micrometers

What is Indoor PM?

Particulate matter is a complex mixture of solid and/or liquid particles suspended in the air and is found in all indoor environments. However, particles, especially 10 micrometres in diameter or smaller, are exceptionally concerning because these particles are inhalable. 

Common Health Effects

Exposure to inhalable particles can affect both your lungs and your heart. Small particles, less than 10 micrometres in diameter, get deep into your lungs and possibly into the bloodstream. People with heart or lung diseases such as coronary artery disease, congestive heart failure, asthma or chronic obstructive pulmonary disease (COPD), children and older adults may be at greater risk from PM exposure.

PM exposure is also linked to a variety of health impacts, including:

  • Eye, nose and throat irritation
  • Aggravation of coronary and respiratory disease symptoms
  • Premature death in people with heart or lung disease

Sources of Indoor PM

It's important to understand that the PM found indoors includes particles that come from outdoor air and particles. Common sources of Indoor PM include:

  • Indoor dust
  • Cooking
  • Combustion activities:
    • Burning candles
    • Use of fireplaces
    • Use of unvented space heaters
    • Kerosene heaters
    • Tobacco
    • Other smoking products
  • Printers
  • Biological contaminants
    • Mould
    • Plants
    • Pests
    • Animals

How to reduce exposure to Indoor PM

The best way to reduce PM indoors is by removing its sources. Examples are:

Outdoor air: 

  • Keep windows closed when outdoor pollutants (i.e. car exhaust, smoke, road dust, pollen, factory emissions, wildfires) are high
  • Use portable air cleaners
  • Install higher efficiency filters in your HVAC and ventilation system

Indoor dust:

  • Frequently clean and ventilate
  • Regularly change HVAC filters
  • Upgrade HVAC filters


  • Improve ventilation and filtration during cooking can reduce exposure to indoor PM
  • Ensure to turn on a wall or ceiling exhaust fan and open windows or doors (when safe)
  • Vent the range hood to the outdoors


  • Prohibit indoor smoking
  • Ensure proper ventilation when burning candles
  • Do not use wood-burning appliances indoors

Biological contaminants:

  • Keep windows closed on high pollen days
  • Frequent cleaning
  • Prevent mould, dust mites and cockroaches


2. Carbon Monoxide (CO)

a carbon monoxide detector mounted to house ceiling

What is Carbon Monoxide?

Carbon monoxide is an odourless, colourless and toxic gas; it is impossible to see, taste or smell the toxic fumes. The effects of CO2 exposure can vary significantly from person to person depending on age, overall health and the concentration and length of exposure.

The average outdoor air concentration of CO2 is in the order of 300 to 400 ppm.  Indoor levels are usually higher due to the CO2 exhaled by building occupants. Indoor combustion appliances, particularly gas stoves, can also increase CO2 levels.

Common Health Effects

Depending on the extent of exposure to CO2 and the level of concentration, various health effects are possible.

At low concentrations, it is common for healthy people to feel fatigued. For people with heart disease, it is common to experience chest pain. 

At moderate concentration, individuals can experience the following;

  • Angina
  • Impaired vision 
  • Reduced brain function 

At higher concentrations, CO2 can be fatal. Individuals can experience the following;

  • Impaired vision and coordination
  • Headaches
  • Dizziness
  • Confusion
  • Nausea
  • Flu-like symptoms that clear up after leaving home
  • Fatal at very high concentrations

Sources of Carbon Monoxide

Indoors, CO2 is mainly produced through the respiration (breathing) of occupants, but can also come from:

  • Cigarette smoking
  • Unvented or poorly vented fuel-burning appliances
  • Leaking chimneys and furnaces

Outdoor sources of CO2 that are also found indoors include;

  • Forest fires
  • Combustion of fossil fuels
  • Animal and plant respiration
  • Organic matter decomposition

The level of CO2 in indoor air depends on three main factors:

  • Ventilation 
  • Indoor sources of CO2
  • The outdoor CO2 concentration

How to reduce exposure to Carbon Monoxide

You can lower levels of CO2 indoors by increasing ventilation and controlling the sources of CO2.

  • Consider purchasing a vented space heater when replacing an unvented one
  • Install and use an exhaust fan vented to the outdoors over gas stoves
  • Opening windows when possible


3. Volatile Organic Compounds (VOCs)

someone using a cloth and spray bottle to wipe counter tops

What are Volatile Organic Compounds?

Volatile organic compounds (VOCs) are emitted as gases from certain solids or liquids. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. Organic chemicals are widely used as ingredients in household products. Paints, varnishes and wax all contain organic solvents, as do many cleaning, disinfecting, cosmetic, degreasing and hobby products. Fuels are made up of organic chemicals. All of these products can release organic compounds while you are using them and, to some degree, when they are stored.

Common Health Effects

The ability of organic chemicals to cause health effects varies greatly from those highly toxic to those with no known health effects.

As with other pollutants, the extent and nature of the health effect will depend on many factors, including the level of exposure and length of time. Among the immediate symptoms that some people experience soon after exposure to some organics include:

  • Eye and respiratory tract irritation
  • Headaches
  • Dizziness
  • Visual disorders and memory impairment

Exposure to some VOCs can cause:

  • Fatigue 
  • Nausea 
  • Dizziness 
  • Headaches 
  • Breathing problems 
  • Irritation of the eyes, nose and throat

Children, seniors, pregnant people and people with existing health conditions, such as asthma, chronic pulmonary disease or bronchitis, are at greater risk. 

Sources of Volatile Organic Compound

  • Cooking, especially frying
  • Cigarette smoke
  • Candles and incense
  • Composite wood products, such as some furnishings and flooring materials
  • Building materials such as paint, glues and varnish
  • Household products, such as air fresheners and cleaning products
  • Infiltration from attached garages, such as from vehicle exhaust
  • Combustion sources such as improperly vented fireplaces, wood stoves, gas stoves and furnaces

How to reduce exposure to Volatile Organic Compounds

You can reduce exposure to VOCs in your home by:

  • Increasing ventilation when using products that emit VOCs
  • Meeting or exceeding any label precautions
  • Use integrated pest management techniques to reduce the need for pesticides
  • Use household products according to the manufacturer's directions

    4. Asbestos

    House roof

    What is Asbestos?

    You can be exposed to asbestos when a home or building is being renovated or demolished when doing car maintenance and drinking water.

    There are no significant health risks if materials containing asbestos in your home are:

    • Left undisturbed
    • Isolated in an attic
    • Sealed behind walls and floorboards
    • Tightly bound in products and are in good condition

    Common Health Effects

    Breathing in asbestos fibres can cause cancer and other diseases, such as:

    • Asbestosis 
      • Scarring of the lungs, which makes it difficult to breathe
    • Mesothelioma 
      • A rare cancer of the lining of the chest or abdominal cavity
    • Lung cancer 

    Sources of Asbestos

    Asbestos is found in: 

    • Building materials: 
      • Roofing shingles
      • Ceiling and floor tiles
      • Paper products
      • Asbestos cement products
    • Friction products:
      • Automobile clutch
      • Automobile brake
      • Transmission parts
    • Heat-resistant fabrics
    • Packaging
    • Gaskets
    • Coatings

    How to reduce exposure to Asbestos

    In a workplace setting, you should report any damage to materials containing asbestos to the appropriate authority, such as your occupational health and safety manager. Additionally, Public and commercial building owners should keep an inventory of asbestos-containing materials to inform tenants, management and contractors.

    In your home, you can reduce your risk of exposure by hiring a professional to test for asbestos before doing any:

    • Renovations or remodelling
    • Demolitions
    • Additions

    If a professional finds asbestos, hire a qualified asbestos removal specialist to remove it before beginning work.


    5. Biological Pollutants 

    particulate matter floating through air

    What are Biological Pollutants?

    Biological contaminants include bacteria, viruses, animal dander and cat saliva, house dust, mites, cockroaches, and pollen. Relative humidity of 30-50 percent is generally recommended for homes. Standing water, water-damaged materials or wet surfaces also serve as a breeding ground for moulds, mildews, bacteria and insects. House dust mites, the source of one of the most powerful biological allergens, grow in damp, warm environments.

    Common Health Effects

    Biological pollutants can trigger allergic reactions, such as hypersensitivity pneumonitis, allergic rhinitis and asthma. 

    Common health symptoms caused by biological pollutants are: 

    • Sneezing
    • Watery eyes
    • Coughing
    • Shortness of breath
    • Dizziness
    • Lethargy
    • Fever
    • Digestive problems

    Children, the elderly and people with breathing problems, allergies, and lung diseases are particularly susceptible to disease-causing biological agents in the indoor air.

    Sources of Biological Pollutants

    Biological contaminants are or are produced by living things. For example, biological contaminants are often found in areas that provide food, moisture, or water. 

    Common sources:

    • Bacteria are carried by people, animals, and soil and plant debris.
    • Mould 
    • Pollens, which originate from plants
    • Viruses, which are transmitted by people and animals
    • Household pets, which are sources of saliva and animal dander (skin flakes)
    • Viruses and bacteria

    How to reduce exposure to Biological Pollutants

    To reduce exposure to such biological contaminants, maintain good housekeeping and regulate heat and air conditioning equipment. Adequate ventilation and good air distribution also help. The key to mould control is moisture control. 

    Other tips include:

    • Install and use exhaust fans in kitchens and bathrooms that are outdoors.
    • Ventilate the attic and crawl spaces to prevent moisture build-up.
    • Keep the house clean.