Plants: Natural Air Purifiers?

Plants absorb carbon dioxide and release oxygen through photosynthesis, increasing humidity by transpiring water vapour through microscopic leaf pores. They can also passively absorb pollutants on the external surfaces of leaves and the root-soil system. Some plants, called hyperaccumulators, absorb high levels of pollutants without poisoning themselves. However, the small scale at which they do so hardly makes them a remedy for indoor gas build-up. Relying on plants to clean indoor air is likely a lost cause, as the amount of air that circulates through a home, office, or other indoor environments in a given period is astronomically higher than the amount of air that even hundreds of plants could ever clean.

Plants absorb carbon dioxide and release oxygen

Trees, for example, are particularly effective at storing carbon, making the planting of trees a significant way to combat climate change. In addition to carbon dioxide, plants can also absorb other gases and toxins from the air and transform them into less toxic substances, a process known as phytoremediation. This process has been applied to large-scale pollution clean-up projects, but its effectiveness on a smaller scale, such as indoor environments, is limited.

While plants do improve air quality, their ability to purify indoor air is not as significant as that of a typical air purifier with filtration media. Thousands of cubic feet of air pass through a home each day, and a single plant or even hundreds of plants can only remove a minuscule amount of particulate matter from that air. Additionally, the contribution of the plant microbiome, the populations of microorganisms that live with plants, to the removal of airborne pollutants is not yet fully understood.

Recent research has shown that plants absorb about 31% more carbon dioxide than previously thought, and understanding the processes involved in carbon fixation is essential for predicting future CO2 levels in the atmosphere and the potential for natural carbon sequestration.

Plants can absorb pollutants on their leaves and root systems

The leaves of plants can absorb a variety of airborne pollutants, such as formaldehyde, benzene, trimethylamine, and xylene, thereby reducing their concentrations in indoor environments. NASA research scientists revealed in a 1989 report that common houseplants perform pollution absorption efficiently under low-light conditions. The University of Minnesota relates that NASA scientists determined that 15 to 18 plants in 6- to 8-inch pots cleanse the air in an 1,800-square-foot home.

The root systems of plants can also play a role in absorbing pollutants. For example, the shrubby dwarf Mugo pine (Pinus mugo pumilo) absorbs petroleum in USDA zones 3 through 8. The 30-foot-tall and wide Eastern redbud tree (Cercis canadensis), for USDA zones 4 through 9, absorbs perchloroethylene and vinyl chloride and is especially petroleum-tolerant.

While plants can absorb pollutants on their leaves and root systems, it is important to note that they do so on a small scale, and relying on plants to clean indoor air of particulate matter is likely ineffective. Thousands of cubic feet of air pass through a home each day, and plants can only remove a minuscule amount of particulate matter from all that air.

Some plants are hyperaccumulators, absorbing high levels of pollutants

Plants improve air quality by absorbing carbon dioxide and releasing oxygen through photosynthesis. They also passively absorb pollutants on the external surfaces of leaves and on the plant root-soil system. However, plants are usually chosen for indoor use based on their aesthetic appeal and ease of maintenance rather than their air-purifying abilities.

While plants do absorb gases and pollutants from the air, their impact on indoor air quality is limited. The amount of air that circulates in an indoor environment is significantly higher than the amount of air that plants can clean. Nevertheless, plants have been used in large-scale pollution clean-up projects, a process known as phytoremediation.

Some plants are hyperaccumulators, capable of absorbing and concentrating extremely high levels of metals in their tissues. Hyperaccumulators can grow in soil or water with high metal concentrations, absorbing them through their roots. These plants have a genetic advantage, as the toxic levels of heavy metals in their leaves can deter herbivores.

Thlaspi caerulescens (T. caerulescens), for example, is a zinc hyperaccumulator found in Zn/Pb-rich soils. It has the ability to extract vast quantities of heavy metals from the soil. When compared to a non-hyperaccumulator species, Thlaspi ochroleucum, T. caerulescens had much higher shoot/root zinc concentration levels.

The ability to hyperaccumulate is determined by environmental exposure and the expression of specific genes, known as hyperaccumulation genes (HA genes). These genes are found in over 450 plant species and enable plants to uptake and sequester metals such as arsenic, cobalt, iron, copper, cadmium, lead, and zinc at 100-1000 times the concentration found in other species.

Hyperaccumulating plants are of interest for their potential to extract metals from contaminated sites, returning the ecosystem to a less toxic state. This process, known as phytomining, involves growing hyperaccumulator plants, then harvesting them to extract the metals from their tissues.

The right plants can reduce indoor pollution

Plants can improve air quality through several mechanisms. They absorb carbon dioxide and release oxygen through photosynthesis, increase humidity by transpiring water vapour through microscopic leaf pores, and passively absorb pollutants on the external surfaces of leaves and on the plant root-soil system.

However, plants are usually chosen for indoor use based on their appearance and ability to survive with little maintenance, rather than their air-purifying abilities. While plants do absorb gases and pollutants from the air and metabolise them into oxygen and other less toxic compounds, they do so on a small scale that is insufficient to combat indoor gas build-up.

Nevertheless, research suggests that integrating plants with smart sensor networks and other computerised technologies could improve indoor air quality in a cost-effective and sustainable way. For example, NASA research scientists revealed in a 1989 report that common houseplants perform pollution absorption efficiently under low-light conditions. The University of Minnesota also referenced this NASA research, noting that 15 to 18 plants in 6- to 8-inch pots can cleanse the air in an 1,800-square-foot home.

Some examples of hyperaccumulating plants include peace lilies, which absorb toxins such as benzene and formaldehyde, and leafy weeping fig trees, which clean the air of formaldehyde, toluene, and xylene. The dwarf date palm is another hyperaccumulator, absorbing pollutants such as benzene, cadmium, formaldehyde, and lead.

While plants alone may not be enough to combat indoor air pollution, the right plants integrated with smart technologies can indeed reduce indoor pollution.

Plant-based technology could be a cost-effective way to clean air

Plants have been proven to absorb gases and chemicals from the air, soil, and water and transform them into less toxic substances. This process, known as phytoremediation, has been applied to large-scale pollution clean-up projects. However, it is important to note that plants do not purify indoor air in the same way that a typical air purifier with filtration media does.

While plants can absorb pollutants, the scale at which they do so is relatively small, making them less effective for addressing indoor gas build-up. Nevertheless, certain plants have been identified as hyperaccumulators, capable of absorbing high levels of pollutants without being harmed. Examples include the peace lily, which absorbs toxins such as benzene and formaldehyde, and the dwarf date palm, which hyperaccumulates benzene, cadmium, formaldehyde, and lead.

The integration of plant-based technology with smart sensor-controlled air cleaning technologies has been proposed as a potentially cost-effective and sustainable way to improve indoor air quality. This approach combines plants with computerized technologies, leveraging their ability to absorb toxins and increase humidity. However, limited research has been conducted to quantify the effects of different plant species on indoor air quality, and more studies are needed to optimize this approach.

To make plant-based technology a viable solution for air purification, further understanding of plant physiology and plant-microbe interactions is necessary. By identifying the plant species and microorganisms that are most effective at removing specific pollutants, we can enhance the efficiency of phytoremediation. Additionally, genetic engineering and gene editing technologies can be employed to improve plants' ability to break down pollutants.

In conclusion, while plants alone may not be sufficient for indoor air purification, plant-based technology has the potential to be a cost-effective component of a comprehensive air cleaning system. By integrating plants with smart sensors and computerized technologies, we can create more sustainable and healthier indoor environments. Further research and innovation in this field are warranted to fully realize the benefits of plant-based air purification.

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