Glossary of air quality terms

Explore our glossary of air quality terms

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The quality of the air we breathe has a direct impact on our health. We talk a lot about the impact of outdoor pollutants, but there are also many sources of air pollution inside our homes. Since this is an important public health issue and it can be difficult to find your way through all the terms used, we offer you this glossary which, we hope, will help you to see things more clearly.

Humid air

Relative humidity is the percentage of water vapor in the air. For maximum comfort, we aim for a level of between 30 and 50% indoors.

Below this level, the air is considered dry. On the other hand, a rate higher than 50 indicates that the air is humid. A hygrometer (also called a humidity sensor or relative humidity indicator) is used to measure the percentage of humidity in the air. This instrument is readily available at hardware stores.

Humid air can cause damage to your property: condensation, bad odors, swelling of wood or flooring, appearance of stains on the ceiling or walls.

It can also have a negative impact on your health. Indeed, humidity is one of the most common causes of poor air quality in homes, as it promotes the emergence and proliferation of mold and dust mites.

As a result, occupants of homes with high humidity levels are more likely to experience symptoms such as eye, nose and throat irritation, coughing, nasal congestion, wheezing, asthma and allergic reactions. Mould can also cause serious respiratory infections in vulnerable individuals, such as children, the elderly and people with health problems.

Fortunately, it is possible to control humid air. In the summer, the use of a dehumidifier or an air conditioner will help reduce the humidity level, while in the winter, we will focus on better indoor ventilation.

Stale air

In opposition to healthy air coming from outside, stale air (impure, polluted) refers to indoor air that has already been breathed and that, by remaining stagnant in a closed environment, becomes loaded with polluting micro-particles.

These pollutants can come from materials (wood, fabrics, coatings, plastics) as well as from human activity in the home (drying clothes, preparing meals, etc.). In addition, if the ambient humidity level is too high, problems related to the presence of airborne molds can be added.

Stale air can contain: carbon monoxide, ozone, sulfur dioxide, nitrogen dioxide, volatile organic compounds (VOCs), heavy metals, allergens, microbes, bacteria, molds, and other undesirable particles.

Stale air, which is low in oxygen, can cause many daily discomforts (fatigue, dizziness). It can also cause more serious health problems (asthma, allergies, lung diseases, cancer).

To avoid any inconvenience, it is recommended to air the different rooms of the house by opening the windows at least 10 minutes per day. To improve indoor air quality, it is also important to properly maintain your air conditioning and heating system by replacing the filters at the suggested intervals.

Nitrogen Dioxide

Nitrogen dioxide (or NO2) is a reddish-brown gas with a strong odor. It is a common pollutant in the air, both indoors and outdoors. NO2 is released during combustion processes. It can have harmful effects on health and the environment (acid rain).

The sources of nitrogen dioxide are many and varied: emissions from cars, trucks and buses, industrial processes, power plants using fossil fuels, tobacco smoke.

Inside our homes, NO2 comes mainly from gas appliances (gas stoves, water heaters, fireplaces, furnaces, generators).

Depending on the level of exposure, nitrogen dioxide can reduce lung function, aggravate asthma symptoms and increase the risk of respiratory symptoms (coughing, wheezing).

Fortunately, you can reduce your exposure to NO2 by adopting certain habits:

  • Turn on the exhaust hood over the gas stove when cooking and preferably use the back burners. Make sure the air is properly exhausted to the outside.
  • Maintain your fuel-burning appliances, have them professionally inspected at least once a year, and change the filters at the recommended intervals.
  • Avoid running your vehicle engine or using gas appliances in an enclosed environment, such as a garage.

Air cleaning

The term “air cleaning” refers to processes or actions that purify and clean indoor air to reduce exposure to airborne fine particles and improve the quality of the air we breathe.

In a well-maintained home, fine particles come mainly from the outside through ventilation systems, open doors and windows or cracks in the air. Indoor mold, tobacco smoke, cooking processes, renovations and poorly maintained furnaces can also generate microparticles, as can the various pollutants naturally present indoors.

There are several solutions for air purification. Ventilation and airing of indoor spaces can help reduce the level of fine particles in the air.

Heating, ventilation and air conditioning units and air purifiers can also be beneficial. The filters they use can capture dust, particles and other impurities, helping to clean the air. At, our furnace filters (Carrier, Honeywell and others) provide an optimal level of filtration until the last days of use. To maximize their efficiency and performance, it is recommended that they be replaced at the intervals suggested by the manufacturer.

Fungal Infection

Some fungi can cause infections in humans, which are called fungal infections.

Fungi (molds) reproduce by spreading microscopic spores. These spores are invisible to the naked eye.

In some cases, the spores remain airborne and can be inhaled. In other situations, they are present on the ground. Fungal infections usually reach the lungs or the skin.

Preventing the appearance and proliferation of molds will reduce the risk of fungal infection and prevent the many symptoms associated with the presence of molds (eye, nose and throat irritation, coughing, wheezing, asthma, etc.).

But how do you do it? First of all, it is important to quickly correct any cause of water accumulation or infiltration, such as a broken pipe, a flood or a sewer backup, because stagnant water encourages the appearance of mould. It is also important to ensure that the humidity inside the home is maintained at an optimal level (between 30 and 50%). In some cases, the use of a dehumidifier may be necessary.

To improve air quality, it is also important to regularly maintain your heating, ventilation and air conditioning equipment and to choose good quality furnace filters (Carrier, Honeywell and others) and humidifiers filters.

Improving air quality is possible

Now you know a little more about the impact of humid air, stale air, nitrogen dioxide and mold on the quality of the air you breathe.

Above all, you know that it is possible to breathe clean and healthy air by adopting small simple gestures and by doing a good maintenance of your appliances.

At, our commitment to air quality includes a selection of filters that meet high quality standards and offer an optimal level of filtration. Order yours today!