Air quality is determined by the composition of the volume of air under consideration. Generally, the normal composition of air is 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, trace amounts of other gases, and around 1% water vapour. Substances not naturally found in the air or found in the air at higher than usual concentrations are pollutants which are detrimental to air quality.
In healthy house terms, we are interested in indoor air quality; a lack of ventilation can concentrate indoor air pollution and our living patterns bring about prolonged exposure to pollution. So what pollutants are we at risk from?
Radon is a gas that in certain regions (especially those where granite bedrock predominates), emanates naturally from the Earth. It is a carcinogen, wherein the risk to health lies. Researchers have estimated that radon in the home causes approximately 20,000 lung cancer deaths in the European Union each year, around about 1,000 of those in the UK. [Ref: BBC News]
As it exudes from the ground it can become trapped inside the sealed envelope of a building and increase in concentration. Where there is a significant risk from radon emissions, the risk is usually mitigated through the employment of a radon barrier as part of the floor construction.
Formaldehyde (the stuff used in embalming), which is toxic to humans in high concentrations, can be emitted from building materials such as plywood and foam insulations and furnishings such as carpeting. Minimising the use of such materials will mitigate the risk.
Volatile Organic Compounds (VOCs) can be introduced through selection of certain products. Within and around the home, common artificial sources of VOCs include paint thinners, dry cleaning solvents, wood preservatives and petroleum fuels. The nature of the risk varies inline with the exact compound; they are variously carcinogenic or causative of respiratory problems. It is also important to note that VOCs are a significant outdoor air pollutant and contribute to global warming.
Although no longer produced, the lead in lead based paints can degenerate into dust and be inhaled. Lead is poisonous and can cause damage nerve connections.
Air pollution can also be introduced intentionally, the use of air fresheners, burnt incense, scented cleaning items all add foreign bodies to the air breathed within the home. Similarly, open fires, wood-burning stoves and other non-sealed carbon fuelled heat sources can smoke particulates to the air, both inside and out.
Also related to carbon fuelled heating systems, carbon monoxide is a colourless, odourless and lethal gas, poisoning from which is often caused by faulty ventilation and chimneys.
A further concept of interest is that of Indoor Surface Pollution (ISP). ISP is defined by reference to the Fleece Factor – the area of the building that is carpeted, curtained and in other ways clothed with fabric and the Shelf Factor – the area of open shelving or other storage in the building. By consideration of these, in relation to the people and pets that reside within the space and the nature and frequency of cleaning we can begin to gain an appreciation of the nature and quantity of air-borne microscopic particles, potential effects of these and methods for minimising them.
Many of these pollutants can be introduced during construction of the building; therefore, we should allow a new build to air out for a period of perhaps 2-4 weeks prior to occupation.
The reduction of air pollutants and associated quality of the air are factors over which we have control through the choices made when designing, building, maintaining and living in our homes.