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Peace lily on a windowsill

Ordinary potted house plants can potentially make a significant contribution to reducing air pollution in homes and offices, according to new research led by the University of Birmingham and in partnership with the Royal Horticultural Society (RHS).

During a series of experiments monitoring common houseplants exposed to nitrogen dioxide (NO2) – a common pollutant – researchers calculated that in some conditions, the plants could be able to reduce NO2 by as much as 20 per cent. The results are published in Air Quality Atmosphere and Health.

The researchers tested three houseplants commonly found in UK homes, easy to maintain and not overly expensive to buy. They included Peace lily (Spathiphyllum wallisii), Corn plant (Dracaena fragrans) and fern arum (Zamioculcas zamiifolia).

Each plant was put, by itself, into a test chamber containing levels of NO2 comparable to an office situated next to a busy road.

Over a period of one hour, the team calculated that all the plants, regardless of species, were able to remove around half the NO2 in the chamber. The performance of the plants was not dependent on the plants’ environment, for example, whether it was in light or dark conditions, and whether the soil was wet or dry.

The plants we chose were all very different from each other, yet they all showed strikingly similar abilities to remove NO2 from the atmosphere. This is very different from the way indoor plants take up CO2 in our earlier work, which is strongly dependent on environmental factors such as nighttime or daytime, or soil water content.

Lead researcher Dr Christian Pfrang

The team also calculated what these results might mean for a small office (15 m3) and a medium-sized office (100 m3) with different levels of ventilation. In a poorly ventilated small office with high levels of air pollution, they calculated that five houseplants would reduce NO2 levels by around 20 per cent.  In the larger space, the effect would be smaller – 3.5 per cent, though this effect would be increased by adding more plants.

While the effects of the plants in reducing NO2 are clear, the precise mechanism by which they do this remain a mystery. Dr Pfrang added: “We don’t think the plants are using the same process as they do for CO2 uptake, in which the gas is absorbed through stomata – tiny holes – in the leaves. There was no indication, even during longer experiments, that our plants released the NO2 back into the atmosphere, so there is likely a biological process taking place also involving the soil the plant grows in – but we don’t yet know what that is.”

Dr Tijana Blanusa, principal horticultural scientist at the RHS and one of the researchers involved in the study said: “This complements RHS efforts to understand scientific detail behind what we know to be a popular passion. Understanding the limits of what we can expect from plants helps us plan and advise on planting combinations that not only look good but also provide an important environmental service.”

In the next phase of the research, the team will be designing sophisticated tools for modelling air quality indoors encompassing a much wider range of variables. The new project, funded by the Met Office, will use mobile air quality measuring instruments to identify pollutants and test their effects in both residential and office spaces, producing a wealth of data to inform the tool’s development.

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  • For media enquiries please contact Beck Lockwood, Press Office, University of Birmingham, tel: +44 (0)781 3343348.
  • The University of Birmingham is ranked amongst the world’s top 100 institutions. Its work brings people from across the world to Birmingham, including researchers, teachers and more than 6,500 international students from over 150 countries.
  • Gubb et al. (2022). ‘Potted plants can remove the pollutant nitrogen dioxide indoors.’ Air Quality Atmosphere and Health.
  • About the RHS: The Royal Horticultural Society, the world’s leading gardening charity, was founded in 1804 by Sir Joseph Banks and John Wedgwood. Our vision is to enrich everyone’s life through plants, and make the UK a greener and more beautiful place. This aspiration underpins all that we do, from inspirational gardens and shows, through our scientific research, to our education and community programmes such as Campaign for School Gardening and Britain in Bloom. We produce key publications, hold a world-class collection of horticultural books and botanical art, and sell the very best plants and gardening gifts.
  • The RHS is fundraising £40m to transform our gardens, outreach and education facilities, which includes redeveloping our flagship RHS Garden Wisley and opening a new garden, RHS Garden Bridgewater, in 2021. We are solely funded by our members, visitors and supporters. RHS Registered Charity No. 222879/SC03826