As a matter of fact, we are now living in an era of intense pollution; coming up with remedial solutions is as such crucial. One way to turn our heads is towards the natural assets that we already have in the environment. There has been some interest, debate and research into the use of plants to purify air. But first, we need to understand why we need to purify our air and how plants are involved in it.

Air pollution

Air pollution is the release of toxic substances into the environment that eventually affects our health and our environment. It is estimated that around one-third of chronic respiratory diseases is due to air pollution. While we are more aware of outdoor air pollution like the release of chemicals from factory chimneys and vehicles, indoor air pollution is also prevalent.

Confined places and air pollution

Materials in houses such as furniture, paint, paper, electronic devices emit harmful substances like formaldehyde and benzene. These chemicals can cause drowsiness, nausea, eye/nose/throat irritation to asthma. The issue of indoor air pollution becomes alarming when the area in question is compact and stuffed. Studies have shown that proper ventilation in these closed areas reduces symptoms of sicknesses.

How do plants purify air?

The way that plants work is that air, with whatever it contains, enters the leaves through the stomata (small pores under a leaf). In the same way, harmful substances like benzene enter the leaves and are trapped within molecules inside them. Other toxins mix with tree materials, form larger masses and then fall to the ground. Furthermore, bigger particulate matters fall onto the leaf surfaces and get stuck to them. In addition to all this, air diffuses into the soil around the root system (and everywhere else for that matter); microorganisms that live in the soil and around the roots take up this air for their activities.

Why is the air near forests so pure?

Ever wondered why the air near forest areas is so clean compared to urban regions? There is less pollution, true, but air moves around and eventually gets to these forests. It is the mass of trees and plants that help in trapping the noxious products. The leaves absorb the polluted air, trap dangerous gases and then release fresh oxygen. Microbes also help in this task, enhancing their capacities to do so over time. So plants, trees, can, in fact, help to purify air.

Now, this is an outdoor scenario: hectares of forests in an open setting. The conditions are not the same as in an indoor environment. The temperature, moisture, season, wind speed, direction, the age of the plants, types of trees all play an important role in this air purification mechanism.

NASA uses plants to purify air

This research work in 1989 has attracted a lot of attention ^[1] and misconception.

The highlights of the study are as follows:

• 12 potted plants (English Ivy, Pot mum, Janet Craig, Ficus, Bamboo palm, Gerbera Daisy, Mother-in-law tongue, Warneckei, Chinese evergreen, Marginata, Peace lily and Mass cane) obtained from nurseries were used to test their capacities to remove benzene, trichloroethylene and formaldehyde from the air.
• They were placed in 2 small chambers (W*-76 cm by D-76 cm by H-76 cm) and 2 bigger chambers (W-76 cm by D-76 cm by H-153 cm).
• Contaminants in air were measured using gas chromatography-mass selective detector analysis; microbial counts were made by counting colonies; plants in activated carbon were also used to test the air.
• The plants were studied over a two years’ period and samples were regularly taken to note the changes.

Using NASA as bait

This study is the basis for most indoor-plants –purifying-air articles. The 12 plants used in the study are the ones suggested as air purifying agents. Others come from the book, How to grow fresh air, by the same researcher, Dr Wolverton ^[2]. Unfortunately, most people using this information are not specialists in the field and misuse it. Using NASA as bait to write about the purifying properties of indoor plants makes sense but it is not totally true. You can’t put a mother in law plant in a 5 m by 5 m room and expect it to start removing all toxins from the air. The environment and the criteria used in the study were very different than what we have in a normal room.

Fact or bait then?

To be sure, all plants can actually trap harmful airborne products in the above-mentioned ways, some better regarding certain chemicals, some others. What was actually found during the project was that the roots and the microbes in the soil helped in trapping the harmful elements. It wasn’t only the plants that were thus involved in the study, but the soil and microbes too. So obviously, putting a bunch of rose flowers in your room will not better your air.

The results suggest that plants can be used for bioremediating air pollution over long periods of time and when they are used in great quantity. Recent studies on the matter have revealed that the rate of absorption of harmful pollutants by indoor plants is actually too low to be qualified as air purifying agents ^[3]. In contrast to this, other studies have shown that plants do have the capacity to remove air pollutants by a factor of two ^[4]. So all in all, mixed results are seen, but to say that flower bouquets can purify the air is downright ridiculous.

*W- width, D- diameter, H-height

References:

1. Wolverton, B.C., Johnson, A. and Bounds, K. (1989). Interior landscape plants for indoor air pollution abatement. NASA, John Stennis Space Centre, Science and Technology Laboratory – Final Report. [pdf] Available at https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930073077.pdf [Accessed 15/06/2018]
2. Wolverton, B.C. (1997). How to grow fresh air: 50 house plants that purify your home or office. Penguin Books.
3. Schmitz, H., Hilgers, U. and Weidner, M. (2008). Assimilation and metabolism of formaldehyde by leaves appear unlikely to be of value for indoor air purification. New Phytologist Trust, 147 (2), pp. 307-315
4. Wang, Z. and Zhang, J.S. (2014). Experimental investigation of the formaldehyde removal mechanisms in a dynamic botanical filtration system for indoor air purification. Journal of Hazardous Materials. 280, pp. 235-243