In high income countries such as the UK, it is estimated that we spend around 85-90% of our time indoors, with approximately two thirds of this in our homes. It therefore follows that most of our exposure to air pollutants happens indoors, whether those pollutants are generated indoors or outdoors.
However, most of the air pollutant measurements, emissions characterisation, air quality modelling and air pollutant regulations focus on the outdoor environment (where we spend on average less than 10% of our time).
The World Health Organisation (WHO) recently stated that exposure to indoor and outdoor air pollution was one of the greatest risks to human health, and that improving air quality was necessary to reduce the global incidence and impact of diseases such as lung cancer, stroke and asthma.
Recognition of the significance of exposure to pollution indoors has grown over the last thirty years, particularly following the COVID-19 pandemic. The importance of good ventilation and healthy indoor air quality received much attention. However, research, evidence, advice and regulations still focus predominantly on outdoor air pollution.
If we wish to mitigate accordingly and reduce exposure to air pollution, we need to understand its sources and transformations, both indoors and outdoors.
There are numerous sources of indoor air pollution in a typical home.
These include activities such as cooking, cleaning, air freshener or scented candle use, DIY activities, building and furnishing materials and people themselves through breathing and even interactions of air pollutants with oils in their skin.
Outdoor air pollutants can enter buildings through doors, windows, and cracks in the building fabric. Here, they combine with indoor emissions to form a complex chemical mixture, about which relatively little is known. However, there is evidence that some of the products of this chemical mixture are harmful to health.
Ventilation rates continue to decrease in new buildings in line with energy efficiency measures. Whilst this is understandable from a climate change perspective, lower ventilation rates have been associated with adverse health effects indoors.
As we continue to address climate change through reduced energy use, we must avoid making indoor air quality worse for future generations through improving our understanding of the tensions between these connected issues.
This is particularly important given the current drive to build significant numbers of new homes.
So, what are the potential solutions to improve indoor air quality?
Air cleaners are often suggested as one possible route for cleaner air in buildings. However, they must be selected and used carefully. If a building is already well ventilated, they are not needed.
If an air cleaner is deemed to be necessary, it is important to use one that does not generate chemical pollutants through its operation as many of them do. The Government’s SAGE group produced a report during the COVID-19 pandemic that contains some useful advice on this topic.
House plants have also been suggested as a way of cleaning up the air. However, there is no evidence to suggest that they can do this efficiently in a typical building, with typical sources of pollution.
Plants have other benefits, particularly psychological, but they are not going to clean up the air to any significant extent.
So what can you do?
The first thing to do is always, to remove pollutant sources. Consider whether you need to use items in the home that release pollutants, or at least consider limiting their use.
If you must use them (and we all need to cook and clean of which, more below), then increase ventilation rates while you do. It is nearly always possible to open windows to do this.
If you live on a busy road, then open windows on the opposite side of the house to the road or avoid ventilation during rush hours. If natural ventilation isn’t possible, then consider an air cleaning device, but read the SAGE report first.
When cleaning, you can use liquid cleaners instead of sprays. Sprays turn the cleaning product into aerosols, which are much easier to breathe in.
Beware of products that claim to be ‘chemical free’ – water is a chemical!!
Also, products that are labelled as ‘green’ or ‘natural’ often contain as many volatile compounds as more regular cleaners. This is because many of the common fragrance chemicals are derived from natural products. The smell of lemons for instance, comes from a chemical called limonene, which is a key component of many personal care products. It is very reactive and that applies equally if it is sourced naturally from a lemon, or synthetically in a laboratory.
It is also important that you follow the manufacturers’ instructions with cleaning products – don’t use too much and never mix products. Also, always ventilate as you clean.
For cooking, always use an extractor fan and if you don’t have one, open a window whilst cooking and for 10 minutes afterwards.
If you have an extractor fan, make sure it ventilates outdoors and not back into the kitchen.
Use the rings at the back, as the extractor fan is more efficient there. If you are renovating your kitchen, then switch to electric/induction rather than gas. Gas hobs generate more particulate matter as they operate, given the naked flame.
Try not to fry in oil too often, but if you do, then make sure you ventilate well as you do so.
For activities that generate moisture in the home (cooking, showering, drying clothes), it is also important that you ventilate to prevent moisture from building up indoors and allowing the formation of damp and mould.
Finally, you can pass on these tips to people you know. Most people are unaware of indoor air pollution and the importance of good ventilation in the home.
Passing on these key messages will help to reduce their exposure to air pollution in their homes.
We thank Nicola Carslaw, Department of Environment and Geography, University of York.
Nicola presented as part of the October 2023 CO Research Trust Lecture "Education, Ventilation, Information: improving air quality in our schools"
The lecture can be viewed in full below: