Indoor Air Quality (IAQ) in the Home

By reasonable estimates, the urban population (which means 60% of us) spend 90% of their time indoors. This makes the quality of indoor air a very significant issue! Taking into account the airtightness now required by Building Regulations, it means that any build up of internal pollutants needs to be managed proactively. Pollutants arising internally can be biological or chemical in nature. Where cooking is carried out using solid fuels, the release of carbon monoxide (CO) can be a problem, but this is not a widespread issue in the UK. Although CO₂ is present in ambient air at around 400 ppm without cause for concern, it is at increased levels of this gas that adverse effects to humans become noticeable. At around 2,000 ppm, behaviour is marked by yawning and a lack of concentration, whereas at 5,000 ppm any occupant can expect to suffer from nausea and headaches. Whilst an excess of CO₂ causes temporary discomfort, is not responsible for long-term conditions. This cannot be said about any of the remaining environmental pollutants which are dealt with below!

The main types of harmful pollutant arising indoors are Volatile Organic Compounds (VOCs). These can be present in household cleaning products. The major source of VOCs are chemicals which vaporize from the surfaces of fabrics and furnishings, an effect which is especially prevalent in the first year in the life of a building. The most aggressive VOCs are benzene and formaldehyde, which are both carcinogenic. It should be noted that high levels of CO₂ have the effect of accelerating the release of VOCs.

The build up of internal pollutants is kept at bay by ventilation. This involves twin processes: the evacuation of foul indoor air and the introduction of “fresh” air from outside. It is therefore important to gauge the quality of such external air, as this will inevitably be reflected by the IAQ. It is worth taking a moment to identify the most harmful pollutants which are widespread externally:

  • Particulate Matter, PM₁₀ or even PM₂.₅. These tiny suspended particles arise largely from engine combustion and brake wear. The smallest particles are able to penetrate the tiny recesses of lung tissue, pass into the blood stream and thence make their way to the brain. This is extremely harmful to children, as cognitive development is impaired. In later life, PMs are causal to cardiac conditions and strokes.

  • Ozone, O₃. This is a gas formed by the photochemical reaction, in the presence of sunlight, of a mixture of airborne VOCs and ambient gases. It is an irritant which affects airway tissues and exacerbates asthma conditions, especially in the young.
  • Nitrogen dioxide, NO₂. This is another by-product of combustion. It is associated with a number of respiratory conditions, including asthma, chronic obstructive pulmonary disorder (COPD) and pneumonia, making children more susceptible to all of these in later years.
  • Polycyclic aromatic hydrocarbons (PAHs). These are also a by-product of combustion, but this time affecting children at the very earliest stages. With exposure to PAHs either pre- or post-natally, children will become predisposed to asthma and allergic reactions.

With such an array of harmful influences waiting to gain admittance, it could be said that any form of ventilation in urban surroundings becomes a balancing act: it must reduce the ingress of outdoor pollutants, whilst preventing the build up of the indoor variety. Techniques to reduce the impact of external contaminants are constantly being reviewed. Besides filtration of incoming air, they include the optimising of intake positions (facing away from pollution sources), green garden barriers and traffic reduction schemes.

Any forms of pollution have a disproportionately greater effect on children. Their rate of respiration is up to six times that of adults, weight for weight, so that malign respiratory agents exert a powerful influence. Windows of vulnerability occur at the foetal stage and early childhood, causing long-term problems which can be cardiovascular, respiratory and neurological in nature.


This stores up a major problem for society: that if the health and neurological development of many of the nation’s children be compromised in such ways, then their life chances will be reduced, they will not fulfil their potential and they will become a precocious burden on the Health Service.

As adults who may or may not be entrusted with the care of the young, we must nevertheless always remain aware of airborne pollutants and their potential for harm. The World Health Organisation (WHO) has confirmed air pollution to be the number one environmental health risk facing us all, accounting for 7 million premature deaths annually worldwide. Therefore, sources of airborne pollution should never be tamely accepted as part of life, but should be energetically resisted and determined action taken to eliminate them at source or diminish their impact.


Author: David Bradbury, Content Manager

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