Air Quality

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Causes & sources

Causes of Poor Indoor Air Quality

Three major reasons for poor indoor air quality in buildings:

  1. The presence of indoor air pollution sources
  2. Poorly designed, maintained, or operated ventilation systems
  3. Uses of the building that were unanticipated or poorly planned for when the building was designed or renovated.

1. Sources of Air Pollution

The most important factor influencing indoor air quality is the presence of pollutant sources. Commonly found pollutants and their sources include:

  • Fine and ultra fine dust like tobacco smoke, combustion processes and furnaces
  •  Asbestos from insulating and fire-retardant building supplies; formaldehyde from pressed wood products
  • Organics compounds from building materials, carpet, and furnishings, cleaning materials and activities, restroom air fresheners, paints, adhesives, printers and copying machine
  • Biological contaminants from dirty ventilation systems or water-damaged walls, ceilings, and carpets
  • Micro organic (viruses and bacteria) contaminants from humans and animals like influenza, chickenpox, measles, german measles, mumps, smallpox, whooping cough, meningitis, diphtheria, pneumonia, tuberculosis, psittacosis and legionnaire's disease.
  • Fungi and spores contaminants like aspergillosis, acute allergic alveolitis, histoplasmosis and coccidioidomycosis
  • Airborne pollen from trees, grasses and wheeds
  • Pesticides from pest management practices

2. Ventilation Systems

Mechanical ventilation systems in buildings, mostly the large ones, are designed and operated to supply the building with fresh air and discharge the high levels of carbon dioxide (CO2) to the outdoors. Recent systems are multifunctional and are designed also to heat and cool the air, and in some cases not only to draw fresh air in but also re-circulate the air throughout the building.

If the mechanical ventilation system, disregarding type, functionalities and features, is poorly designed, operated or maintained, this ventilation system becomes a major source problems in several possible ways.

Poor ventilation can cause diverse air quality issues that affect health, comfort and well-being. Often ventilation is designed to consider only CO2, Relative Humidity levels (%RH) and temperatures, while ignoring air pollutants. Other ventilation systems are designed to have low energy consumption, yet at the expense of air quality.

Some practical examples of indoor air quality problems arising from ventilation systems in buildings:

  1. In an effort to save energy, ventilation systems are set on lower capacities, which reduces the total amount of fresh air drawn into a building. The result is: ventilation systems are not used to bring in adequate amounts of outdoor air.
  2. Low attention to air supply or air return vents may cause an inadequate ventilation. That is since sometimes, air supply and return vents within each room may be blocked or placed in such a way that outdoor air does not actually reach the breathing zone of building occupants.
  3. Improper design pf the building or installation may result that the air intake and exhaust are too close to each other, resulting in pollutants (including high concentration of dust, microbes and CO2) are re-entering the building.
  4. Improperly located outdoor air intake vents can also bring in air which is highly contaminated due to industrial emissions, traffic emissions from automobile and truck exhaust, boiler emissions, fumes from dumpsters, or even air exhausted from the restrooms of the same building.
  5. Ventilation systems can be a source of indoor pollution themselves by spreading biological contaminants that have multiplied in cooling towers, humidifiers, dehumidifiers, air conditioners, the inside surfaces of ventilation duct work.
  6. Finally, conventional air filters (standard integrated in ventilation systems) can be a source of indoor pollution themselves by spreading biological contaminants. That is since conventional filters are made of textile, which in addition to them collecting dust and dirt, they capture humidity, which turn the filters surface into ideal growth environment for microbes and pathogens.

3. Use of the Building

Indoor air pollutants can be circulated from portions of the building used for specialized purposes, such as restaurants, print shops, and dry-cleaning stores, into offices in the same building. Carbon monoxide and other components of automobile exhaust can be drawn from underground parking garages through stairwells and elevator shafts into office spaces.

In building and installation phase and processes, buildings originally designed for one purpose, therefore, the initial attention is drawn to the building function, purpose of use and total number of inhabitants. Yet, the building may end up being converted to use as office space or different purpose, other than the original function. If installations are not properly modified during building renovations and expansion, the room partitions and ventilation system can contribute to indoor air quality problems by restricting air re-circulation or by providing an inadequate supply of outdoor air.