Indoor Air Quality

What is indoor air quality and why to measure it?

In general, indoor air quality (IAQ)  refers to the environmental characteristics inside buildings that may affect human health, work performance or well-being.  IAQ should be monitored, because people in Central Europe spend on average 90 percent of their time indoors today. Every day, people breathe in 10 to 20 m³of air, depending on their age and how active they are. This corresponds to a mass of 12 to 24 kg of air. This is far more than the mass of food and drinking water that a person consumes every day.

In contrast to outdoor air, indoor air is recycled continuously causing it to trap and accumulate (air)pollutants. IAQ characteristics are the concentrations of pollutants in indoor air, as well as air temperature and humidity (sometimes barometric pressure, too).
Poor indoor air quality contributes to both short and long term health issues which can lead to tiredness, general malaise, decreased productivity or loss of working hours. Typical symptoms associated with poor indoor air quality include nose, throat and eye irritation, headache, nausea, dizziness, and fatigue. In some cases continuous exposure to bad indoor air quality can lead to acute and chronic respiratory illnesses including asthma, lung cancer, pneumonia, systemic hypertension, and much more. Below we show a list of major sources and potential health effects of indoor air pollution.

What is an interior (indoor space)?

Indoor space is defined as flats with living rooms, bedrooms, handicrafts, sports and cellar rooms, kitchens and bathrooms, as well as workspaces in buildings which are not subject to the scope of the Hazardous Chemicals Control Ordinance with regard to hazardous substances, such as offices. This also includes interiors in public buildings (hospitals, schools, day-care centres, sports halls, libraries, restaurants, theatres, cinemas and other public event rooms) as well as the interiors of motor vehicles and public transport.

While limit values according to the Hazardous Chemicals Control Ordinance apply to workplaces where hazardous substances are handled, this does not apply to the indoor areas mentioned above. A contamination with formaldehyde in the air of an office room caused by outgassing from furniture containing chipboard should be regarded as a residential pollution and not as a workplace pollution, for example in the chemical industry.

Factors contributing to poor indoor air quality

Gasses and respirable particulates in the indoor air are the primary sources that contribute to poor IAQ. Sources can include inadequate ventilation, poorly maintained ventilation systems, wood/coal stoves and open fire places, non-vented gas heaters, vehicle exhaust emissions from outside the building or a garage, building materials, flooring materials (e.g. carpets), furniture, solvents, cleaning products etc.
The actual concentrations of these pollutants can also be amplified by other factors including poor ventilation, humidity, and temperature.

Major Indoor Air Pollutants

PM – Particulate Matter

Major Sources:
Cigarettes, wood and coal stoves, fireplaces, aerosol sprays (deodorants and hair sprays) house dust, outside air pollution

Potential Health Effects:
Eye, nose and throat irritation, increased susceptibility to respiratory infections, bronchitis, lung cancer

CO2 – Carbon Dioxide

Major Sources:
Excessive building occupancy and inadequate ventilation, sick building syndrome (SBS)

Potential Health Effects:
Fatigue, eye, nose and throat irritation,  headache, general chest discomfort

CO – Carbon Monoxide

Major Sources:
Non-vented or malfunctioning gas heaters, wood/coal stoves and open fire places, tobacco smoke and vehicle exhaust emissions from the outside or from garages within the house

Potential Health Effects:
Headache, nausea, angina, vision problems and limited mental functioning, Fatal at high concentrations

HCHO – Formaldehyde

Major Sources:
Pressed wood products e.g. plywood and MDF, furnishings, wallpaper

Potential Health Effects:
Eye, nose and throat irritation, headache, allergic reactions, cancer

VOC – Volatile Organic Compounds

Major Sources:
Aerosol sprays (e.g. deodorants and hair sprays) , solvents, glues, cleaning agents, pesticides, paints, moth repellents, air fresheners, dry cleaned clothing and treated water

Potential Health Effects:
Eye, nose and throat irritation, headache; loss of coordination; damage to liver, kidney and brain; various types of cancer

NO2 – Nitrogen Dioxide

Major Sources:
Fuel-burning stoves (wood, kerosene, natural gas, propane, etc.) Fuel-burning heating systems (wood, oil, natural gas, etc.) Tobacco use

Potential Health Effects:
Respiratory effects including airway inflammation in healthy people and increased respiratory symptoms in people with asthma. NO2 creates ozone which causes eye irritation and exacerbates respiratory conditions

Biological Components (bacteria, viruses, fungi, animal dander, dust mites, arthropods )

Major Sources:
House dust, pets, bedding, poorly maintained air conditioners, humidifiers and dehumidifiers, wet or moist structures, furnishings, ventilation systems

Potential Health Effects:
Allergic reactions; asthma, eye-, nose- and throat irritation; influenza and other infectious diseases, scabies


Major Sources: Soils and rocks under buildings, some earth-derived construction materials, groundwater

Potential Health Effects:
Lung cancer


Major Sources:
Damaged or deteriorating insulation, fireproofing and acoustical materials, general building materials

Potential Health Effects:
Asbestosis, lung cancer, mesothelioma and other cancers

Methods for assessing IAQ

There are two main methods for assessing the quality of indoor air:

  • Real-time (continuous) measurements (monitoring). Real-time monitors can be used for detection of pollutant sources and provide information on the variation of pollutant levels throughout the day. Aristoteles Consulting is using equipment for real-time IAQ monitoring.
  • Integrated sampling with subsequent laboratory analysis. Integrated samples, normally obtained during the 8 working-hours for offices or 24 hours in apartments and houses, can provide information on the total exposure level of a specific pollutant or a group of pollutants.

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