In a new study from the University of Birmingham, experts have confirmed that potted houseplants can substantially improve indoor air quality in homes and offices. The researchers found that houseplants were particularly effective in reducing levels of nitrogen dioxide.
“Nitrogen dioxide (NO2) is a significant pollutant in both outdoor and indoor environments with exposure linked to serious respiratory illnesses, decreased lung function and airway inflammation,” wrote the study authors.
“Here, we investigate whether potted plants can contribute as a simple and cost-effective indoor air pollution mitigation technique.”
The researchers conducted a series of experiments in which they monitored common houseplants that were exposed to nitrogen dioxide (NO2). The results suggest that plants can remove NO2 by up to 20 percent, depending on the conditions.
The study was focused on three species of houseplants: Spathiphyllum wallisii (peace lily), Dracaena fragrans (corn plant), and Zamioculcas zamiifolia (fern arum). The plants were individually placed in chambers which contained an amount of NO2 that could be realistically found in an office on a busy street.
The experiment showed that all of the plants, regardless of species, were able to remove around half the NO2 in the chamber within just one hour.
“The plants we chose were all very different from each other, yet they all showed strikingly similar abilities to remove NO2 from the atmosphere,” said lead researcher Dr. Christian Pfrang.
“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.”
Based on the results of the experiment, the experts estimated how the plants would affect air in a small- or medium-sized office with different levels of ventilation. The team calculated that in a poorly ventilated small office with high levels of air pollution, five houseplants could reduce NO2 levels by around 20 percent.
The ability of houseplants to quickly and effectively remove nitrogen dioxide are clear, but the underlying mechanism remains a mystery.
“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,” explained Dr. Pfrang.
“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 is the principal horticultural scientist at the Royal Horticultural Society (RHS) and one of the researchers involved in the study. He said the research 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.”
The study is published in the journal Air Quality Atmosphere & Health.