All houseplants help purify the air

Empty advertising promises: Plants are bad air purifiers

For a study that appeared in the Journal of Exposure Science and Environmental Epidemiology, Waring and his co-author analyzed twelve studies from the past decade that tested a total of 196 houseplants.

The studies that concluded that a small houseplant can absorb various toxins were all carried out under laboratory conditions. According to Waring, a typical experiment setup would involve placing a plant in a small chamber and exposing it to volatile organic compounds (VOCs). The experiments differed depending on the density of the gas mixture and its duration. One of them showed that common ivy could remove two thirds of the formaldehyde from the air mixture in their chamber.

According to Waring, the problem with these experiments is that the chambers in the laboratory are not comparable to a typical room or office environment.

Many of the blogs and sales sites that advertise air-purifying plants refer to a study by NASA from 1989. In it, plants were placed in approximately 60 by 60 centimeter chambers with various gas mixtures that were circulated by a fan. The now 30-year-old study showed that plants can reduce VOCs in small, airtight containers. And this study is also why some customers somewhat overestimate the capabilities of their houseplants, experts say.

"We are not saying that the data from the experiments are incorrect," says Waring. They are just that - experimental.

From the laboratory to the office

To estimate how plants affect a typical household environment, Waring calculated the Clean Air Delivery Rate (CADR) for each plant species. This indicates how much clean air an air purifier releases into a room during a certain period of time.

By standardizing the study results using the CADR figure of merit, the researchers were able to assess how well a plant cleaned the indoor air compared to mechanical air purifiers or simply an open window.

“Plants remove VOCs, but they do it so slowly that they cannot keep up with the normal air exchange mechanisms in a building,” says Waring.