85% of countries experienced indoor air quality worse than outdoor for more than 6 months of 2022
Dyson’s first Global Air Quality Connected Data project examined the indoor air quality data from more than 2.5m connected Dyson air purifiers
- Two-thirds of countries experienced higher annual average indoor PM2.5 levels compared to outdoor in 20222 showing the levels of pollutants in homes.
- All countries’ monthly average indoor PM2.5 levels exceeded WHO long-term exposure guidance for at least 6 months of the year3, including Ireland which exceeded WHO limits every month.
- Winter was the most polluted season in all geographies, with Ireland peaking during the months of December and March.
- Overall, in an average 24h period, the most polluted time (PM2.5 levels) fell between 6pm and midnight, coinciding with times when people are usually in their homes.
- Irish homes saw a spike in indoor air pollution between 7pm and midnight
DUBLIN, 11.01.2024. Today, Dyson unveils the results of its first Global Connected Air Quality Data project¹, the largest study of indoor air quality globally. The project studies indoor air quality information collected by more than 2.5 million Dyson Purifiers from 2022 to 2023 to landscape air quality in real homes across the world, to a granularity never before seen. Whilst data is based on homes with Dyson Purifiers and as such is not nationally representative, the volume of data reaches into the tens of billions of data points and paints a picture of indoor air quality in cities and countries globally beyond the scale that has been achievable to date.
From a wealth of data, this project focuses on two types of pollutant – PM2.5, and Volatile Organic Compounds (VOCs). PM2.5 refers to particles as small as 2.5 microns in diameter; a typical human hair measures around 70 microns in diameter. These particles are invisible to the naked eye, can be inhaled and are an area of increasing scientific and health research. Sources include combustion – wood burners, or gas cooking and heating – pollens, pet dander and dust. VOCs are gas pollutants including Benzene and Formaldehyde which can be emitted from activities like cleaning or cooking as well as from products including deodorants and body sprays, candles, furniture and furnishings.
“Our connected air quality data allows us insight into the real problem of indoor air pollution in homes across the world. This gives us a direct understanding of the challenges Dyson Purifiers face in real environments and the knowledge to engineer ever-better machines to tackle those challenges. But the data we capture isn’t just an engineering tool – on an individual basis, this data is shared back through the MyDyson app in real-time and via monthly reports, to help our Owners improve their air quality understanding.”
Matt Jennings, Engineering Director for Environmental Care
Nearly all homes experienced indoor air quality worse than outdoor
All but four countries studied exceeded outdoor PM2.5 levels for six months or more², including the UK and Germany where indoor levels exceeded outdoor PM2.5 monthly averages for eleven months of 2022, and China, Australia, France, Austria, Canada and Spain whose homes exceeded outdoor air quality every month in 2022. Only homes in India, Norway, Poland and Finland saw PM2.5 levels consistently below outdoor levels (fewer than six months in 2022). In February, seven countries noted the highest indoor PM2.5 level compared to outdoor; In Germany, indoor PM2.5 pollution was more than double outdoor, and in Austria indoor PM2.5 in the same period was 95% higher. 20 out of 31 studied countries saw an annual average indoor air quality that exceeds the outdoor air quality, when considering PM2.5; Austria, Spain, Australia, Canada, the UK, Denmark and the Netherlands are some notable inclusions.
At city level, the annual average indoor PM2.5 in homes in Milan was more than 2.5 times the outdoor PM2.5 level – a discrepancy higher than any other city studied. After Milan comes Shenzhen (97% higher indoors), Amsterdam (76%), Seoul (53%), Madrid (50%), Melbourne (40%), Vienna (37%), Singapore (36%), New York (35%) and Tokyo (24%). 21 cities of 35 studied experienced annual average PM2.5 levels higher indoors than outdoors. Looking monthly, eight cities studied saw higher PM2.5 levels indoor compared to outdoor for every month of the year: Shenzhen, New York, Melbourne, Milan, Rome, Seoul, Vienna and Amsterdam.
Ireland is ranked 28th globally for indoor/outdoor ratio of PM2.5 levels with China, Austria, and Spain at the top.
fig. 1. Top 10 cities by indoor-outdoor pollution ratio
Winter sees highest particle (PM2.5 & PM10) pollution levels
As winter approaches, we will spend an increasing amount of time in our homes. Throughout the year, we spend 90% of our time indoors – at home, work, or for leisure. Dyson purifier data showed that the winter period was the most polluted in terms of particle pollution globally. Colder weather means we seal our homes more, keeping windows shut and possibly heating with combustion, like gas heating, woodburners or even lighting candles. However, not all countries experiencead the most particle pollution during winter. March was the most polluted month for 8 countries, followed by January, for 7 countries. In the UK, where March was the most polluted month, the average PM2.5 level was more than double July, the month with lowest recorded monthly pollution level.
fig. 2. Global annual particle pollution trend, shown seasonally (inc. VOCs) (with WHO trend line in red)
"We all think of air pollution as being an outdoor or roadside problem. Indoor air pollution research is growing, but continues to be underdeveloped. Dyson's findings give us a valuable insight into the real pollution levels in homes across the world, helping us to understand the patterns of pollution daily, monthly and seasonally. The Dyson data is an incredibly powerful education tool and the opportunities for positive impact are boundless – understanding the pollution around us is the first step to reducing our pollution exposure.”
Professor Hugh Montgomery, Chair of Intensive Care Medicine at University College London, and Chairperson of Dyson’s Scientific Advisory Board
PM2.5 annual average: A surprising global picture
When looking globally at the data from Dyson connected purifiers throughout 2022, there are some surprising results when ranking countries on their average PM2.5 level. Whilst India and China occupy the top two spots, likely due to the relationship between indoor and outdoor air quality, Romania ranks 6th, Italy 8th and Poland 9th and Austria 10th. The UK (22nd) outranks the United States (26th), Canada (27th) and Australia (28th), but Germany and France rank higher, at 20th and 22nd respectively. Indoor PM.5 annual averages in all countries studied exceeded the WHO annual guideline for PM2.5 (5 µg/m3) – India by 11 times, China by 6 times, Turkey and UAE by 4 times, and South Korea, Romania, Mexico and Italy by 3 times.³
At a city level, the top five cities by average annual PM2.5 are all in Asia – Delhi, Beijing, Shanghai, Shenzhen and Busan, followed by Istanbul, Dubai, Seoul, Mexico City and Vienna. Similarly to the country-level data, every city studied exceeded the WHO long-term or annual exposure guideline for PM2.5 (5 µg/m3) – even Sydney, which takes last place in the rankings, registered an annual average PM2.5 level of 6.78 µg/m3. Delhi homes exceeded the WHO guideline by 14x, Beijing by more than 6x and Shanghai more than 5x. Osaka, Los Angeles, Paris, Tokyo, Amsterdam, Munich, Taipei and Dublin homes all experienced double the WHO annual guideline for PM2.5.
fig. 3. Annual pollution levels vs WHO guideline in red line
VOCs annual average: Europe claims top rankings
In contrast to PM2.5, it is European countries that experienced the highest annual VOC levels according to Dyson Purifiers. Austria tops the list, followed by Romania, Germany, Switzerland, Poland and Turkey. Italy appears in 8th and Ireland in 10th. Many countries that ranked highly for average annual PM2.5 do not rank highly for VOCs: Thailand, UAE, Malaysia and South Korea do not appear in the top half of countries by annual VOCs. In fact, the US, France, Spain and Denmark all rank higher.
Similarly, European cities also experienced high levels of VOCs indoors compared to other regions. Munich is the highest ranked city, followed by Beijing, Cologne, Berlin and Vienna. Only Beijing is in the top five cities for both annual PM2.5 and VOCs, whilst Delhi, Istanbul, Shanghai and Mexico City feature in the top ten for average level of both types of pollutant.
Evening pollution higher than any other time of day
In most countries studied, indoor PM2.5 levels were highest during the evening and night-time hours, coinciding with the time that the majority of people spend in their homes, rather than being out at work, school or elsewhere. PM2.5 levels peak in between 7pm and 10pm in the UK. Exposure is the measure of air pollution concentration over time, which within the air quality research community is a key consideration – a spike of air pollution (a very high level for a short period of time) is not necessarily worse than prolonged exposure to ‘poor’ or even ‘fair’ air quality. Therefore, data from Dyson purifiers suggests that this longer, more polluted period may account for increased exposure to PM2.5 in homes.
Evening pollution was higher than any other time of day in most countries, including Ireland, with spikes between 7pm and 11pm recorded on Irish Air Purifiers. This stat coincides with the time of day that many people spend in their homes.
fig. 4. Global daily PM2.5 levels over time
Low uptake of Auto mode globally
Globally, just 8% of Dyson Purifiers spend more than three-quarters of the time in Auto mode – where the machine constantly monitors the air quality and automatically responds to changing pollution levels – suggesting that Dyson machines in homes across the world are not being used to automatically manage the pollution events in homes these connected air quality data insights show. The US leads the way on proportion of purifiers in Auto mode (14%), with Chicago topping the list of cities, followed by New York, Toronto and Los Angeles. [Markets to insert local comparison between % in Auto mode and AQ awareness/concern stats locally if desired – please avoid any cause-effect conclusions].
Some of the cities with the lowest proportion of machines in Auto mode correlate to those who rank highly in pollution levels on a daily, monthly and average basis – in particular PM2.5 – including Shenzhen (2.2%), Mexico City (2.4%) and Shanghai (3%) which note the three lowest percentages of purifiers in Auto mode.
About the project
The Dyson Global Connected Air Quality Data project analyses more than half a trillion data points to paint a picture of the air quality in real homes around the world, understand user behaviours and compare indoor and outdoor air quality. The total global sample size is 3.4m. In the UK, the national sample size is 149k, and at city level, 39k in London. The indoor air quality studied is based on the location of Dyson Purifiers in homes and as such is not nationally representative.
Indoor air quality data is taken from Dyson Purifiers that are connected to the MyDyson app and in monitoring-only mode – that is, not actively purifying the space. Whilst this reduces the sample size for the calculation, Dyson data scientists can be confident that it is an accurate representation of air quality in real homes, without the impact of Dyson Purifiers actively cleaning the air.
From a wealth of data, Dyson data scientists have focused on PM2.5 and VOC data, analysing the measurements from 1st January to 31st December 2022. Data is collected by the machines every 1 minute, which is time-averaged into averages by hour, day, month, season and year depending on the calculation in question. For all the mean estimates, we consider the 99% credible interval to ensure accurate, statistically significant spatial and/or temporal comparisons.
Outlier machines have been removed as part of data cleansing. For example, machines that are showing extremely high particle pollution in a region where this trend is not reflected across the board, may have a blockage in the sensor which might skew the data readings. These types of outliers have also been removed. A machine “in Auto mode” is determined by it spending >75% of each day in the year in Auto mode. This allows for ~6 hours of the day on manual, which would account for it being used manually in heating or cooling mode.
Machines are not all on for 24 hours a day, for every day of the year. As such, machine data is weighted in line with the proportion of the given time-frame that each machine is on, connected to the MyDyson app and recording data. For example, if a machine is only connected to the MyDyson app for 6 months of the year, the machine would be weighted less than a machine connected year-round.
Outdoor air quality data is sourced primarily from OpenAQ, and from the World Air Quality Project in Shenzhen, Fukuoka, Osaka, Amsterdam and Taipei.
Countries studied: Australia, Austria, Belgium, Canada, China, Czechia, Denmark, Finland, France, Germany, Greece, Hungary, India, Indonesia, Ireland, Israel, Italy, Japan, Malaysia, Mexico, Netherlands, New Zealand, Norway, Philippines, Poland, Portugal, Romania, Saudi Arabia, Singapore, South Korea, Spain, Sweden, Switzerland, Thailand, Turkey, UAE, UK, USA, Vietnam
Cities studied: Amsterdam, Bangkok, Beijing, Berlin, Bristol, Brussels, Busan, Chicago, Cologne, Copenhagen, Delhi, Dubai, Dublin, Fukuoka, Hanoi, Hong Kong SAR, Istanbul, Jakarta, Kuala Lumpur, London, Los Angeles, Lyon, Madrid, Manchester, Manila, Marseille, Melbourne, Mexico City, Milan, Mumbai, Munich, New York, Osaka, Paris, Rome, Seoul, Shanghai, Shenzhen, Stockholm, Sydney, Taipei, Tokyo, Toronto, Vienna
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1. The study captured data from 3.4m connected Dyson Purifiers globally between January and December 2022. No personal data was used in this study, you can find further information on Dyson’s privacy policy here. Data has only been collected from Dyson connected purifiers and therefore is not representative of every home.
2. PM2.5 levels collected from Dyson connected purifiers have been compared to WHO 2021 guidelines for annual and daily PM2.5 exposure, which can be found here: www.who.int/news-room/feature-stories/detail/what-are-the-who-air-quality-guidelines.
3. Indoor pollution recorded by connected Dyson Purifiers vs outdoor data sourced from openaq (https://openaq.org/) and World Air Quality Index (https://aqicn.org/).
