Are homes a source of air pollution?
In this guest piece from Dr Claire Holman, Director at Brook Cottage Consultants, she asks if our homes are a source of air pollution. Dr Holman will be taking part in our retrofit webinar panel – do sign up for updates here.
We spend most of our time indoors, typically around 80 to 90% of the time. With the COVID-19 restrictions many are spending even longer periods in their homes. Yet relatively little is known of pollution levels inside buildings, particularly homes. As the air outside has become cleaner the emphasis is increasingly moving indoors where we are likely to be exposed to a different cocktail of pollutants.
The increasing air tightness of our homes and other buildings, designed to save energy and reduce carbon emissions, has resulted in increasing levels of pollution indoors. There are literally thousands of different chemicals we breathe in; most we know little about their potential health effects.
This pollution comes from outside, through doors, windows, building fabric and mechanical ventilation systems, into the indoor environment. In addition, a wide range of air pollutants are emitted directly inside. But that is not all, many are also formed within buildings from other pollutants. There is evidence that some air purifiers, designed to remove air pollutants, can initiate a chain of chemical reactions that produce toxic pollutants.
Taking just one chemical – formaldehyde. This belongs to a class of chemical compounds known as volatile organic compounds or VOCs. It is probably the VOC of greatest importance, due to its prevalence in the indoor environment and its known health impacts. It is ubiquitous in construction, insulation and decorating products, and wood based furniture. Formaldehyde within these products is released into the building gradually over several years. Levels increase in summer, as the higher temperatures increase the rate of release of the formaldehyde (known as off-gassing). New homes have been found to have particularly high levels.
Formaldehyde is also used in inks and toners, disinfectants, polishes, waxes, washing and cleaning products, textiles, fragrances, and air fresheners. Despite its widespread use, most people will be unaware of it as a pollutant.
There is evidence that formaldehyde is formed within buildings from terpenes such as D-limonene and α-pinene which provide the lemon and pine fragrances used in cleaning products. These reactions can be initiated by ozone, from outside or formed within the building, or by the free radicals formed by some air purifiers.
Short term exposure causes irritation of the eyes, nose, and throat, together with discomfort, lachrymation, sneezing, coughing, nausea and at higher levels, difficulty breathing. Long term exposure to formaldehyde is linked to nasal cancer.
PHE recently published guidelines for formaldehyde. These are, for short term exposure, 100 µg/m3 averaged over 30 minutes and for long term exposure, 10 µg/m3 average over a year. The few studies that have measured formaldehyde levels in homes suggest that concentration are typically in the range around 20-30 µg/m3 averaged over periods ranging from one day to a couple of weeks, with new homes possibly having concentrations 3 to 5 times higher.
The legislation to protect the public from exposure to air pollution largely relates to outdoor air. There is no legal protection for the general public regarding indoor air quality. Employees are covered by Health and Safety at Work legislation, but this may not provide adequate protection for all workers or the general public. The workplace exposure limits are much higher than the air quality standards set to protect human health in the outdoor air and indoor air quality guidelines from the World Health Organization and Public Health England (PHE). For formaldehyde, the PHE short term guideline for formaldehyde is 25 times lower than the Worker Exposure Limit.
The best option for reducing exposure to pollutants such as formaldehyde, which are so widely used, is to use low emitting building materials and products. This requires people to become more widely aware of the risks of poor air quality in their homes and other indoor environments.
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