Determinants of Indoor Air Quality

By ,


Malak Rizk-Bigourd, PhD, Scientific Advisor and Quality Manager Ecomesure

Indoor air quality affects our health without us realizing it. We usually attribute non-specific symptoms like headache, fatigue, and irritation to job related stress or other factors but it is likely that these symptoms are due to poor air quality at the workplace.

These non-specific symptoms are referred to as the Sick Building Syndrome (SBS) if they worsen with the increase in time we spend in the building. Another syndrome due to poor indoor air quality that can have serious, life threatening consequences is Building Related Illness (BRI).

To ensure productivity, it is important to ascertain that the air we breathe is clean. Air monitoring devices can help detect poor air quality but to improve air, it is important to understand the factors that determine the quality of indoor air.

There are three key determinants that control the variations of pollutant concentrations in indoor air:

  • external inputs;
  • internal inputs; and
  • chemical reactivity phenomena.

The effects of these determinants further depend on factors such as temperature, hygrometry, sunlight, ventilation, etc.

The external inputs

The building ventilation, natural (open windows) or controlled (mechanical), plays a major role in determining the impact of outside air on indoor air quality.  While ventilation allows the evacuation of pollutants emitted inside the buildings, it also gives way to outside pollutants. Ventilation ducts themselves emit pollutants such as formaldehyde.

Pollutants like benzene which are rarely released by indoor sources, if found in the indoor air, can be tracked to outside air where they are ubiquitous. Highly polluted outdoor air can significantly increase concentrations of several pollutants such as nitrogen dioxide and fine particles in indoor air.

The internal inputs

Indoor environment  has different types of sources that emit pollutants intermittently or continuously. The intermittent  sources are conditioned by lifestyle and the activities of the occupants. Common one-off sources are cooking (gas), heating mode (open hearth fireplace or oil stove), household cleaning products, scent, candles, incense, and cigarette smoke.

Emission of pollutants especially volatile organic compounds (VOCs), is continuous from buildings materials, furnishing, and decoration. Below are listed the main sources of VOC emissions from the French Building Materials Labeling List (Decree-2011-321, 2011). A wide variety of indoor materials contribute to a continuous supply of VOCs.

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Indoor and Outdoor Air Quality Monitoring and Assessment

Main sources of VOCs in indoor air

FormaldehydeParticleboard, fibreglass, carpet, glue, plywood, insulation material, vinyl wallpaper, gypsum board, air ducts, linoleum flooring, floor polish, ceiling tiles, plasticized flooring, tapestries

Acetaldehyde: Glues, paint, particle board and insulation foams

Toluene: Carpet, solvent-based glue, water-based glue vinyl wallpaper, wallpaper, linoleum flooring, wallcovering, wall coating, chipboard, waxes, plasticized flooring

Tetrachlorethylene: Paint, glue, wall coating, shoe polish, carpet, plastic flooring

Xylene: Glue, wallpaper, flooring, wallcovering, vinyl wallpaper, linoleum, paint, waxes, wallcovering, carpet, laminate flooring

1,2,4-trimethylbenzene: Wallpaper, paint, vinyl wallpaper, floor varnish, concrete pavement, chipboard, PVC flooring, waxes, wood varnishes

1,4-Dichlorobenzene: Wallpaper, glues

EthylbenzenePaint, glue, wall coating, carpet, wax, plastic flooring

2-Butoxyethanol: Floor varnish

StyreneRubber based flooring, latex-based materials, insulation materials, textiles, plastics, paints, carpets

Chemical reactivity phenomena

Like outside air oxidation reactions occur in indoor air. The chemical reactions involving VOCs and ozone lead to the formation of other more oxygenated species that form fine particles. Nicotine from tobacco smoke, reacts with the particles in the presence of ozone, forming other harmful pollutants such as formaldehyde and nicotinaldehyde.


The air we breathe affects our health much more significantly than we can imagine. The 2017 U.S. EPA and the EU EEA reports have attributed hundreds of thousands of deaths last year to air pollution. Poor health due to poor air quality is increasing medical debt by millions everyday. While the outdoor is regulated, indoor air is not. It is critical to be aware and raise awareness around indoor air quality. By choosing to monitor indoor air, we can take better control of our health. Nimonik is promoting Ecomesure air monitoring devices as they are accurate, simple and affordable.