Can indoor plants really clean the air?

You´ve probably heard that plants improve air quality in your home and other indoor environments and can function as air purifiers. Plants are crucial to human life. Through photosynthesis they turn carbon dioxide that we breathe out into fresh air, and they can remove poisonous substances from the air we breathe in. Sadly, however, few studies prove that they actually clean the air around them to an extent that actually makes a difference.

Potted plants do have the ability to remove airborne organisms to some extent (VOC*), but we´re talking about tiny, isolated environments and only after several hours or days. This is according to scientists at Drexel University in the US, who as late as December 2019 published a study in Journal of Exposure Science and Environmental Epidemiology. Michael Waring, Associate Professor of Architectural and Environmental Engineering, examined previous studies and findings and found little evidence that plants do anything to filter pollutants from indoor air.

Many of these studies are limited by unrealistic conditions. Plants were often placed in isolated environments, with a single volatile organic compound (VOC*) deployed to pollute the air. While the VOC levels decreased over hours and days, Waring found that the studies put little emphasis on measuring clean air (CADR) and on how effectively an air purifier is in reality regarding to “cleaning” the space. When Waring converted the study results to CADR, the plants’ abilities to filter pollutants was found to be much weaker than to simply bring fresh air in by opening a window to spread VOC´s. In addition, people are not likely to work or live in such isolated environments.

The concept of plants as natural air purifiers probably originates from a NASA experiment in 1989, which claimed that plants could remove certain air pollutants. As in previous studies, this took place in an isolated environment, which means that the results are not fully applicable in homes and public spaces.

Of course, plants can indeed clean air, but their efficiency is so minimal that Waring believes that between 10 and 1000 plants per square meter of floor space would be required to achieve the same effect as simply opening a window or turning on the ventilation to generate fresh air. We should continue to enjoy plants, but we must realize that they will unfortunately not help us breathe more easily.

*VOC:s are general pollutants in indoor air and several hundred varieties have been identified. Concentration levels are low, around 100 to 1,000 times lower than current work environment guidelines, but usually higher than outdoor environments. Sources of pollution are outdoor air, environmental tobacco smoke, other combustion, building materials and furnishings, consumer products, activities and people. Source: Karolinska Institutet


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