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The importance of air quality

Find out what Airgeek measures and why you should care.

Power plant emissions

CO2
Airborne dust in a living room

PMX
Car exhaust

NO2
Steamy bathroom

RH
Frozen living room windows

T
A smouldering fireplace

CO

Carbon Dioxide (CO2)

Power plant emissions

When we breathe, we exhale carbon dioxide. A small room, or a large room with lots of people in it, fills with CO2 quickly. This makes CO2 an important marker gas: By measuring its concentration in the ambient air, we can tell if the air is fresh or stale, and whether we ventilate sufficiently.[1]

Insufficient ventilation increases the risk of spread of airborne diseases[2], such as the flu. CO2 may also directly assist in the spread of certain viruses.[3]

CO2 also negatively affects our mental performance[4] and interferes with sleep[5].

Aim to keep your CO2 concentration under 800 ppm.

Particulate Matter (PMx)

Airborne dust in a living room

Solid and liquid particles suspended in the air are collectively known as particulate matter (PM). They are divided into classes by their size: PM1 (≤1 μm), PM2.5 (≤2.5 μm) and PM10 (≤10 μm).

PMX exposure has both acute and long-term health effects, ranging from mild respiratory symptoms to premature mortality. Infants, children and older adults with preexisting heart or lung diseases are at greatest risk.[6][7]

Common sources of indoor PMX include burning of candles, woodworking, fireplaces, wood and gas stoves and tobacco smoke. Vehicle emissions, wood burning and industrial emissions are common sources of PMX infiltration.[8]

Keep your long-term exposure to PMX as low as possible. Use range hood at the highest setting while cooking. Extinguish candles with a lid. Open windows only if/when outdoor PMX concentration is below indoor concentration. Consider buying an air purifier.

Nitrogen Dioxide (NO2)

Car exhaust

Nitrogen Dioxide irritates the eyes, nose, throat and the entire respiratory tract.[9] Long-term exposure to ambient NO2 was associated with adverse respiratory effects, especially in children, including reduced measures of lung function and reduced lung function growth.[10]

Gas stoves, tobacco smoke, and engine exhaust and common sources of NO2 pollution, plus various industrial sources.[9] NO2 is also moderately correlated with the presence of other pollutants, such as certain volatile organic compounds (VOCs).[10]

Maintain the annual average NO2 concentration below 30 ppb.[11]

Relative Humidity

Steamy bathroom

High relative humidity promotes the growth of mold, mildew and bacteria. Dust mites thrive in humid environments and trigger allergies.[12]

On the other hand, low relative humidity dries out the mucous membranes, increasing the risk of infections like cold and flu. It may also worsen allergies and asthma.[13]

Low relative humidity also contributes to PMX pollution.[14]

Maintain between 30 % and 50 % relative humidity indoors on average.[15]

Temperature

Frozen living room windows

Temperature under 18 °C exacerbates respiratory conditions such as asthma and increases the risk of respiratory infections.[16] It may also contribute to depression and anxiety.[17]

Temperature above 26 °C has similar effects[18], but may also cause heat exhaustion and metabolic issues. It can also disrupt sleep.[19]

Excessive heating or cooling of outside air can further cause wild swings in relative humidity. It also increases your heating and AC bills.

Keep indoor air temperature between 18 and 26 °C.

Carbon Monoxide (CO)

A smouldering fireplace

Carbon monoxide is a colorless, odorless toxic gas[20] with both acute and chronic health effects.

In high concentrations, carbon monoxide is acutely toxic and causes impairment and death.[20]

Chronic exposure to low concentrations of carbon monoxide causes fatigue, nausea, headaches and flu-like symptoms.[21] Malfunctioning or improperly vented fuel-burning appliances—such as boilers, gas stoves and ovens and fireplaces—often cause carbon monoxide exposure.[20]

Keep your exposure to carbon monoxide (CO) as low as possible. Airgeek is not a CO alarm. A dedicated CO alarm is necessary to prevent CO poisoning. Please read this FAQ.

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References

  1. Residential indoor air quality guidelines: Carbon dioxide, Health Canada, 2021.
  2. About Ventilation and Respiratory Viruses, National Institute for Occupational Safety and Health, 2024.
  3. Ambient carbon dioxide concentration correlates with SARS-CoV-2 aerostability and infection risk, Nature Communications, 2024.
  4. Is CO2 an indoor pollutant? Direct effects of low-to-moderate CO2 concentrations on human decision-making performance, Environmental Health Perspectives, 2012.
  5. Experimental study on sleep quality affected by carbon dioxide concentration, Indoor Air, 2020.
  6. Guidance for fine particulate matter (PM2.5) in residential indoor air, Health Canada, 2012.
  7. Inhalable Particulate Matter and Health (PM2.5 and PM10), California Air Resources Board.
  8. Infographic: What is fine particulate matter (PM2.5)?, Health Canada, 2019.
  9. Nitrogen Dioxide's Impact on Indoor Air Quality, United States Environmental Protection Agency, updated May 2025.
  10. Human Health Risk Assessment for Ambient Nitrogen Dioxide, Health Canada, 2016.
  11. Nitrogen Dioxide & Health, California Air Resources Board.
  12. Indirect health effects of relative humidity in indoor environments., Environmental Health Perspecives, 1986.
  13. Relative Humidity and Its Impact on the Immune System and Infections, International Journal of Molecular Sciences, 2023.
  14. The effect of temperature and humidity of air on the concentration of particulate matter - PM2.5 and PM10, Atmospheric Research, 2024.
  15. Indoor humidity and your family's health, National Asthma Council Australia, 2016.
  16. Low indoor temperatures and insulation, WHO Housing and Health Guidelines, 2016.
  17. Cold homes and mental health harm: Evidence from the UK Household Longitudinal Study, Social Science & Medicine, 2022.
  18. Indoor temperature and health: a global systematic review, Public Health, 2020.
  19. High indoor temperatures, WHO Housing and Health Guidelines, 2016.
  20. Infographic: Carbon monoxide, Health Canada, 2017.
  21. Carbon monoxide poisoning, Harvard Health Publishing, 2023.

Despite our efforts to accurately represent known scientific results concerning air quality, this short material is by no means a replacement for personalized medical advice. If you believe your health may be at risk, please consult a professional about your exact circumstances.