Where is air pollution worst – home, office or construction site?

After finally escaping your stuffy office, you brave your commute and rush past that dusty construction site.

17 Sep 2017

But, as you enter your home and take a deep, cleansing breath, you may have walked into yet another major source of pollution.

The indoor air quality in our homes can be worse than we think – and it could be leading to a wide variety of health problems. Thanks in part to super-efficient modern homes, we may be living in homes filled with volatile organic chemicals such as formaldehyde and benzene that could be having a dangerous long-term impact on our health.

In an effort to better understand air pollution and its effects, we called on two experts in the field of air quality. We asked Professor Ian Colbeck from the School of Biological Sciences at the University of Essex, as well as Paul Dawson, the Global Product Development Director at Dyson, to provide us with the insights they’ve gathered through their work.

What is air pollution?

An expert on indoor air quality, Professor Colbeck explains that both outdoor and indoor air need to be considered when evaluating air quality indoors. He says outdoor air pollution in the present day mostly involves nitrogen oxides and particulate matter from traffic emissions.

Unfortunately, while outdoor air pollution is regularly discussed [1], indoor air pollution gets little attention. This is despite the fact that, as Dawson points out, “Indoor air pollution can be up to five times worse than outside air pollution.”

Indoor air pollution (IAP) is a combination of outdoor polluted air that has seeped inside and the internal pollutants already present. Dawson says Dyson’s “research teams have found that VOCs [volatile organic compounds such as benzene, formaldehyde and trichloroethylene] are a common source of indoor pollutants.”

Professor Colbeck adds further sources of IAP including “tobacco smoke, combustion (such as gas cooking or candles), animals, mould and cleaning products,” as well as solvents from plastics, paints and furnishings.

“Our homes are becoming more sealed – to keep noise out and heat in,” says Dawson, adding, “But it’s not just warmth that gets trapped inside. It can be pollutants and allergens too.” While energy-efficient modern homes can cause a build-up of pollutants, older houses with more ventilation often allow outdoor air pollution to seep indoors.

Carbon dioxide readings around London

To get a better understanding of the levels of air pollution we come across daily, we asked four volunteers across London to help us conduct some case studies. We asked them to measure dust particles – an important measure of pollution – as well as carbon dioxide (CO2) levels in the places they visit on a daily basis.

To make it easier to compare outdoor and indoor pollution levels, we’ll focus solely on the participants’ CO2 measurements, taken using the TSI 7575 Q-Trak [2] air quality monitor. While carbon dioxide is often naturally present in the home at safe levels, it can be surprisingly easy to create a build-up that could have a significant effect on our health and well-being.

Our participants included a personal trainer, an office worker, a construction worker and a stay-at-home mother. With three of the participants being based in the suburbs of London, the expectation was that the study would show reassuringly low levels of pollution, well within normal levels. Needless to say, we were extremely surprised by the results.

The highest readings:

For most of our participants, their highest CO2 readings were during their commute. The highest level of CO2 was 2284 ppm, recorded by Ana, an office worker, in a packed train at Baker Street Station.   

Professor Colbeck explains that “The main source of CO2 is human respiration. The large number of passengers in a confined space results in elevated CO2 levels.” He also pointed out that CO2 isn’t harmful at low concentrations, and is naturally present at levels around 400 ppm.

He noted that CO2 levels between 1000-2000 ppm can cause drowsiness, while levels between 2000-5000 ppm can cause worrying symptoms including headaches, sleepiness, nausea and increased heart rate. With more than 29 million people using Baker Street Station each year, Ana’s alarmingly high reading on the packed train is concerning for many of us who regularly use London’s public transport network.

On the positive side, our construction worker recorded surprisingly low levels of carbon dioxide. His highest CO2 reading at work was 384 ppm, demonstrating the effectiveness of air quality control measures such as those used in his industry. In contrast, CO2 levels inside his home in Croydon were slightly higher, peaking at 490 ppm.

Comparing highest and lowest readings:

We used the results of our study to help us compare the outdoor pollution our participants encounter during their day, and the indoor pollution they face during the commute, at work or at home.

See the results below:

Dyson Air Pollution ComparisonBromley

Outside of their commutes, Cecile – a teacher and stay-at-home mum during the holidays – recorded the highest CO2 reading at her home in leafy Bromley. Surprisingly, Cecile recorded the highest at-home CO2 reading out of all our participants, despite some of them living in much busier areas such as Notting Hill Gate which only saw a high of 730 ppm.

Cecile explained that her reading of 1172 ppm might be because she left the windows closed that day due to colder weather. Professor Colbeck agrees: “Lack of ventilation will result in CO2 increases. Levels will vary throughout the day as people come and go, and windows are open and shut.”

Dollis Hill

Emma, a personal trainer living in Dollis Hill, found she was exposed to surprisingly less CO2 when at work, compared to when at home. Emma spends most of her working day outdoors as a fitness trainer, during which time her average reading was 783 ppm. Her outdoor readings were far lower than the peak 945 ppm CO2 reading she recorded at home.

King’s Cross

Owen, on the other hand, recorded surprisingly low CO2 levels despite being a construction worker in Central London. He recorded an average of 374ppm of CO2 at work in traffic-clogged King’s Cross, well within safe levels. Coming in far lower than Cecile, Emma or Ana’s results, his readings debunk the myth that construction sites are always problematic when it comes to air pollution.

Want to find out more about our participants’ CO2 readings? Click here to view our graph of the average hourly readings recorded by our participants.

Dust measurements around London

Our volunteers also got some interesting insights into the levels of dust they were exposed to during a typical day, using the TSI DustTrak II [3] aerosol monitor.

Dust measurements involve particulate matter (PM) which is a mixture of solid particles and liquid droplets. PM10 represents the largest size particle (10 micrometres) and has a value of 50 µg/m3 over a 24-hour period and 40 µg/m3 over one year before it becomes dangerous to health.

Our participants found that their commutes exposed them to highest dust levels, a trend that Professor Colbeck is familiar with. “PM concentrations at underground station platforms are consistently higher (2–8 times) than at the street level,” he says, adding, “Expect to see higher concentrations when commuting [whatever your method of transport]”.

What are the health impacts of indoor air pollution?

Poor indoor air quality can lead to a whole host of health issues, while indoor air pollution was attributed to 99,000 deaths across Europe in 2012 [4]. Professor Colbeck explains that the “potential health impacts of IAP can include asthma, respiratory irritation, heart disease, cancer, and sick building syndrome.” Sick building syndrome includes headaches, tiredness and loss of concentration, and can particularly affect office workers. [5]

How can air purifiers help reduce indoor air pollution?

Investing in an air purifier can be an invaluable step when it comes to keeping your home free from air pollutants. Air purifiers work by drawing air into the machine, where filters trap dust and other minute particles including pollen, bacteria, ultrafine particulates, VOCs and even odours. The machine then releases the smooth, purified, clean air back into the home.

Want to improve the air quality in your home? The Dyson fans range uses a patented 360° Glass HEPA filter carefully engineered to trap even the most minute of particles. Investing in a Dyson Air Purifier can help turn every home into a safe haven.


[1] https://www.london.gov.uk/sites/default/files/les_full_version.pdf

[2] TSI’s Q-TRAK™ Indoor Air Quality Monitor 7575

[3] TSI’s DustTrak™ II Aerosol Monitor 8532

[4] https://www.rcplondon.ac.uk/projects/outputs/every-breath-we-take-lifelong-impact-air-pollution

[5] https://www.thebesa.com/news/70-of-office-workers-complain-about-poor-air-quality/

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