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.
Lead researcher Dr Christian Pfrang said: “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 night time or daytime, or soil water content.”
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 percent.
In the larger space, the effect would be smaller – 3.5 percent, 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.