House plants can cut dangerous pollution indoors

The humble house plant could be a key weapon in the battle against indoor air pollution, a new study has found.

Researchers found that house plants including peace lilies and corn plants are able to cut levels of a common pollutant emitted by cars by as much as 20% in homes and offices.

Researchers from the University of Birmingham put common (and inexpensive) houseplants into a chamber full of the pollutant nitrogen dioxide (NO2) - at levels comparable to an office 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.

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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 nighttime or daytime, or soil water content."

The team also calculated what these results might mean for a small office of 15 square metres and a medium-sized office of 100 square metres, 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%.

In the larger space, the effect would be smaller - 3.5%, though this effect would be increased by adding more plants.

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While the effects of the plants in reducing NO2 are clear, the precise mechanism by which they do this remains 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."