People love houseplants for various reasons: They look nice; they add an element of nature to an indoor space; they smell good; they clean the air.
Except, new research has found, they don’t effectively do that last thing.
In the 1970s and 80s, NASA tested ways to clean air inside the Skylab space station and other enclosed spaces. Its conclusion was to add plants.
“If man is to move into closed environments, on Earth or in space, he must take along nature’s life support system,” B.C. “Bill” Wolverton wrote in 1989 NASA report.
The problem with NASA’s research and the studies that followed, said Michael Waring, an associate professor of architectural and environmental engineering in Drexel's College of Engineering, that they were conducted in sealed labs on a small scale.
"Typical for these studies," Waring wrote, "a potted plant was placed in a sealed chamber, into which a single VOC (volatile organic compound) was injected, and its decay was tracked over the course of many hours or days."
Waring and doctoral student Bryan Cummings reviewed a dozen of these studies, spanning 30 years of research, and concluded “the natural or ventilation air exchange rates in indoor environments, like homes and offices, dilutes concentrations of volatile organic compounds — the air pollution that plants are allegedly cleaning — much faster than plants can extract them from the air.”
Their finding were recently published in the Journal of Exposure Science and Environmental Epidemiology.
"This has been a common misconception for some time. Plants are great, but they don't actually clean indoor air quickly enough to have an effect on the air quality of your home or office environment," Waring said.
Waring and Cummings took the data from plant studies and used it to calculate a measure called the "clean air delivery rate," or CADR. They made this calculation for nearly every study and “what they found in every case was that the rate at which plants dissipated VOCs in a chamber was orders of magnitude slower than the standard rate of air exchange in a building — thus proving the plants' overall effect on indoor air quality to be irrelevant,” according to Science Daily.
Using Waring and Cummings' calculations, it would take between 10 and 1,000 plants per square meter of floor space to compete with the air cleaning capacity of a building's air system or even just a couple of open windows in a house.
"This is certainly an example of how scientific findings can be misleading or misinterpreted over time," Waring said. "But it's also a great example of how scientific research should continually reexamine and question findings to get closer to the ground truth of understanding what's actually happening around us."
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