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What is good indoor air?


Indoor air is a hot topic and for a good reason. It becomes more important year by year as outdoor air becomes more polluted and symptoms caused by indoor air become more common.

Did you know that it is possible to measure some 60 to 70 variables from indoor air: temperature, pressure difference, humidity, carbon dioxide levels, particles, VOCs, etc.?

Qualities of good indoor air

Clean air is odourless, colourless, and tasteless. It is rich in oxygen and feels fresh. It does not contain any pollutants harmful to health. Good indoor air does not cause any symptoms typical to indoor air problems, such as tiredness, headaches, itching of the eyes or respiratory symptoms.

If something smells odd when you enter a building, that is a sign of poor-quality indoor air. The smell of a basement, an old house, chemicals, sewers, or vehicle exhaust, as well as the general stuffiness of the air, are the most common signs that the indoor air quality is poor.

Many people like the "fresh smell" of a new building, but that is a sign of VOC gases, volatile organic compounds, in the air – these are released from coatings, glued laminated wood, lacquers and varnishes, fire retardants, paints, and laminates.


Standards and reference and threshold values have been established for good indoor air. These have been determined globally by, for example:

World Health Organization (WHO)

American Conference for Governmental Industrial Hygienists (ACGIH, USA)

Occupational Safety and Health Administration (OSHA, USA)

National Institute for Occupational Safety and Health (NIOSH, USA)

The UK government in Control of Substances Hazardous to Health Regulations 2002 (COSHH)

The German Committee on Indoor Guide Values

European Union – Joint Research Centre IAQ


There is also an alternative way to determine the quality of air.

The world’s best indicator is probably the human body. Feeling well is a “green light” that means that the values are appropriate. Perhaps a definition of good indoor air could be that “a person feels well and does not have any symptoms”.


Unfortunately, many people suffer from daily symptoms caused by poor indoor air. We need approximately 10,000 litres of clean air per day. Without clean air, we can survive for approximately 1 minute, without clean water approximately 24 hours, without clean food for approximately 1 week... This fact gives us food for thought. Most of us can choose what we want to eat and drink, but only a few people have the opportunity to choose what kind of air they breathe.

Where is air the cleanest and why?

Volatile organic compounds are present in every residential and office building. These compounds come from building materials, furnishings, chemicals used in the room (e.g. cleaners and detergents), machine and device emissions (e.g. from printers), compounds released due to the thermal degradation of materials, plants and other organic materials and organisms, and external traffic emissions.

Air that is free of these compounds is mostly found on top of high mountains where there are no plants or other emission sources (Turk and d'Angio, 1962). It is no wonder that alpine air is said to be fresh and clean.

What makes indoor air poor?

A general perception is that indoor air quality problems are a result of moisture damage and the accumulation of mould. According to a study commissioned by the Finnish National Institute for Health and Welfare (THL), moisture problems cause only 3–5% of the problems.


According to a study by Sisäilmayhdistys (Finnish Indoor Air Society), most of the problems are caused by fine and ultrafine particles from outdoor air pollution that people bring with them indoors. It is difficult to determine a single cause of poor indoor air quality as it is usually caused by a combination of factors and calls for a comprehensive approach instead of trying to fix one problem at a time.

Download below the free guide to read what factors impact the quality of indoor air. What are the target values and what is the technical definition of good indoor air?

Download our free guide to learn more about good indoor air quality: