Claims that potted plants can help clean indoor air are overblown, say researchers who reviewed a dozen studies conducted across 30 years.

Sorry, Delhi, where the recent, choking air has prompted a run on nurseries.

“People are searching for such [purifying] plants on Google and other websites. Then they are approaching us with the name and photograph of a plant that fights pollution inside a close area. On an average, over 20-50 such plants are being sold every day,” Subhash Singh, a nursery owner near Yamuna Bank Metro station in Delhi, told India Today during the city’s recent air crisis.

And sorry, Kolkata… and Chennai… and the 13 other Indian metros that typically make the world’s top 28 most polluted cities.

“This has been a common misconception for some time,” Michael Waring, Ph.D., an associate professor of architectural and environmental engineering at Drexel University’s College of Engineering in the U.S., said in a press release. “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.”

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Waring led the review of available research, published recently in the Journal of Exposure Science and Environmental Epidemiology, concluding that ventilation clears volatile organic compounds like formaldehyde and benzene — the very compounds plants are thought to clean from the air — exponentially faster than plants absorb them. To determine this, Waring and doctoral candidate Bryan Cummings calculated for each study the “clean air delivery rate,” or CADR, taking into account buildings’ airflow patterns, which they say were previously overlooked.

“The CADR is the standard metric used for scientific study of the impacts of air purifiers on indoor environments, but many of the researchers conducting these studies were not looking at them from an environmental engineering perspective and did not understand how building air exchange rates interplay with the plants to affect indoor air quality,” Waring said in the release.

In fact, the bedrock study of this line of research instead took place in a vacuum chamber, which by definition has no airflow. In such an environment, in 1989 NASA concluded plants could remove cancer-causing pollutants from the air. Waring and Cummings aren’t debunking that finding, but say it’s been taken out of context in a way that has generated trust in plants’ air-purifying powers that isn’t justified.

“This is certainly an example of how scientific findings can be misleading or misinterpreted over time,” Waring said in the release. “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.”

Now, if only we could do that reexamining, questioning and solving of air pollution itself.