Residents of industrialized countries spend over 80% of their time indoors, increasingly in air-tight structures. Although these buildings need less energy for air-conditioning, ventilating, and heating, the build-up of particulate matter and potentially toxic gases, such as ozone, carbon monoxide, and volatile organic compounds, from sources such as office equipment, furniture, paints, and carpets may prove detrimental to human health.
Despite the fact that plants are capable of absorbing toxins and in turn improving indoor air quality, shockingly, it is unclear what plant species are most suited for this purpose and how to enhance the performance of plants indoor.
In a Review published in Trends in Plant Science on April 19, 2018, Frederico Brilli (a plant physiologist from the National Research Council of Italy - Institute for Sustainable Plant Protection) and his collaborators have concluded that a better understanding of plant physiology, combined with integration of smart-sensor-controlled air-cleaning technologies, could provide an economical and sustainable means to enhance indoor air quality.
Plants enhance air quality through a number of mechanisms: they can passively absorb pollutants on the external surfaces of leaves and the plant root-soil system, they ingest carbon dioxide and liberate oxygen through photosynthesis, and they increase humidity by transpiring water vapor through microscopic leaf pores. However, the reason plants are usually chosen for indoor use is not their air-purifying abilities, but their appearance and ability to survive with little maintenance.
“For most of us plants are just a decorative element, something aesthetic, but they are also something else” noted Brilli.
Unfortunately, not much research has gone into quantifying the impacts of various plant species on indoor air quality. In the 1980s, NASA conducted an original study using a simple experimental approach. However, studies with more contemporary, advanced research methods and modeling are yet to be performed.
Additional research is required to recognize the characteristics of the highest performing plant species in indoor environments, including their physiology (that is, CO2 assimilation rate), anatomy, and morphology (that is, leaf size and shape). Brilli remarks that studies could illustrate how to “optimize the use of plants indoors, in terms of how many plants per square meter we need to reduce air pollution to a certain level.”
Research must also be carried out to understand plant microbiomes: the populations of microorganisms (fungi and bacteria) that live with plants on leaf surfaces as well as in the soil. While this microbiome is also involved in the elimination of airborne pollutants, the contribution of various microbial species to eliminating pollutants is not yet known. Certain microbiomes could also have adverse effects on the health of humans, including lung inflammation problems and triggering allergies; therefore, it is essential to know how to recognize and avoid those.
Brilli and his team believe that although plants may not replace modern air conditioning, ventilation, and heating systems, plants incorporated with smart sensor networks and other computerized technologies could make air-cleaning more sustainable and cost-effective. Brilli adds, “plant physiologists should work with architects to improve the green indoors.”