New study says plants have little effect on indoor air quality, better window ventilation

A new study from Drexel University suggests that the decades-old term “plants can improve indoor air quality” is not at all true. After evaluating 30 years of research, two environmental engineers at the school decided it might be better to open the windows and ventilate directly. After all, it takes at least a few hundred trees to purify the air in a small space through plants.

新研究称植物对室内空气质量的影响很小 开窗通风效果更佳

(Pictured: Drexel University, via New Atlas)

As early as 1989, an influential NASA study found that many common indoor plants can effectively remove volatile organic compounds (VOCs) from the air.

The experiment, which was conducted on the surface, was designed to investigate whether plants could help purify the air on the space station, spawning the idea of using plants in homes and office environments to help purify indoor air.

Since then, many experiments seem to confirm NASA’s finding that plants do remove VOCs from indoor environments.

But Michael Waring, a professor of architectural and environmental engineering at Drexel University, and Bryan Cummings, one of his phD students, are skeptical of the consensus.

新研究称植物对室内空气质量的影响很小 开窗通风效果更佳

(Research Match 1)

They note that the vast majority of these experiments are not conducted in a real-world environment. The two wrote in their research paper:

For these studies, it is typical to place potted plants in a sealed chamber (usually cubic meters or less) and inject a single VOC into them, tracking their decay for hours or days thereafter.

To better understand how potted plants removed volatile game compounds from indoor environments, the researchers reviewed more than a dozen published experimental data and then evaluated their efficacy using the clean air delivery rate (CADR) indicators used in the plant.

Waring says CADR is a standard indicator of air purifiers, but many of the people who do this study don’t think about it from this perspective, and they don’t understand the effects of air exchange rates and plant interactions in buildings on air quality.

新研究称植物对室内空气质量的影响很小 开窗通风效果更佳

(Research Match2)

After calculating the VOC rate of plant elimination in each study, they quickly discovered that in the real world, the effects of plants on air quality were almost insignificant.

Large buildings equipped with air handling systems are far more effective in eliminating indoor VOCs than plants.

In the case of removing organic compounds that produced by  a square metre (10.7 square feet) of floor, for example, 1,000 plants will be needed to achieve the same effect.

In addition, most large buildings already exist in the indoor and outdoor air exchange system, can also achieve a good air purification effect.

新研究称植物对室内空气质量的影响很小 开窗通风效果更佳

(Study Match3)

The study noted that the CADR of the normal air purifier was approximately 100 m3 / h (3,531 ft3 / h), while the new study calculated that the CADR for ordinary houses was 0.023 m3 / h (0.812 ft3).

This means that the average house needs to be put into nearly a hundred plants to be equivalent to an air purifier. The researchers even suggest that opening two windows of a room to convection would be much more effective than hundreds of plants.

Of course, this study is not mind-free against the placement of green plants indoors. Some studies, for example, suggest that green planting may have a beneficial effect on the psychology of indoor workers.

Interested friends can move to Journal of Exposure Science and Environmental Operay to read the full study.

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