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Do plants really help Indoor Air Quality (IAQ)? Weeding out fact from fiction

Many articles rave about using plants to clean indoor air. If they can turn carbon dioxide into oxygen, they can turn pollutants into clean indoor air, right? The answer is more complicated than you might think.

You probably learned in science class that plants use photosynthesis to turn carbon dioxide (CO2) into oxygen, making air safer to breathe.

But more dubious is the question of whether plants can do anything to improve your Indoor Air Quality (IAQ) by purifying the air of pollutants.

Many articles rave about using plants to clean indoor air. If photosynthesis can turn a harmful gas into one of the most important molecules we breathe, the notion of plants absorbing pollutants and turning them into clean indoor air doesn’t seem like rocket science, right?

The answer is more complicated than you might think.

So give it to me straight - will plants clean my indoor air?

The short answer to this question? No.

Plants don’t purify indoor air. At least, not the way that a typical air purifier does, using filtration media (such as HEPA or HyperHEPA filters) to remove a high percentage of particulate matter (PM) from the air.

Plants don’t purify indoor air. At least, not the way that a typical air purifier does.

Research does indicate that plants have a limited ability to lower concentrations of certain gases and chemicals from indoor air (more on that in a moment). But relying on plants to clean your indoor air of PM, one of the most significant components of indoor air pollution, is likely a lost cause.

The amount of air that circulates throughout your home, office, or other indoor environment in a given period of time, supplied in large part by outdoor air, is astronomically higher than the amount of air that a single plant, or even hundreds of plants, could ever clean, even if all your windows and doors are closed and your house is completely airtight. Thousands of cubic feet of air pass through a home each day, and plants can only remove a miniscule amount of PM from all that air.

A 2015 study of spider plants (Chlorophytum comosum L.) illustrates this vividly. In this study, researchers placed spider plants in environments with varying levels of exposure to indoor PM, including a dental clinic, a room used to bottle perfume, a typical suburban home, an apartment, and an office.

At the end of a two-month period, researchers found, depending on the environment, that the waxy leaves of the spider plants had accumulated anywhere from 13.62 to 19.79 micrograms of PM per square centimeter of leaf area (μg/cm2).1

That’s almost nothing - a microgram is one millionth of a gram, and human beings breathe about 120,000,000 grams of air each day (about four times that much when you exercise).2

So a single spider plant, which is thought to be one of the better plants for cleaning indoor air (according to this study), removes so little PM from the air that you’d probably need a few thousand of them to clean even a small fraction of indoor air.

A single spider plant removes so little particulate matter from the air that you’d need a few thousand of them to clean your indoor air.

What does the research say about plants and gases?

More significant in the research about plants and indoor air is the effect of plants on indoor volatile organic compound (VOC) build-up.

With the advent of energy-efficient construction, more buildings have become airtight so that heating, ventilation, and air conditioning (HVAC) systems don’t have to work as hard to heat or cool an indoor space, meaning that they use less energy than traditional systems.

This is a good thing for your power usage and electricity bills. However, the hidden cost of energy efficiency is a much lower amount of fresh air exchange with outdoor air. Thus. many gases and compounds commonly found indoors, such as VOCs and even ozone, which largely originates outdoors, can build up to dangerously high levels in energy-efficient homes because there isn’t as much ventilation to disperse them once they get inside.

As a result, researchers have undertaken many studies on plants to remedy this problem. If plants can use CO2 to photosynthesize and create oxygen, shouldn’t they be able to remove other gases from indoor air in the absence of ventilation?

Yes and no.

Plants do indeed absorb gases from the air and metabolize them into oxygen and other, less toxic compounds. Their ability to metabolize gases is so well known that this process has been applied to large-scale pollution clean-up projects, taking on new life under the name phytoremediation. In this process, plants absorb gases and chemicals from air, soil and water through their tissues and either transform them into a less toxic substance or transfer them from one medium to another, such as from water to air.3

But phytoremediation isn’t the antidote for air pollution that one might think. Plants can transform gases into other, often less harmful substances, but the small scale at which they do so hardly makes them a remedy for indoor gas build-up.

Plants do transform gases into less harmful substances, but the small scale at which they do so hardly makes them a remedy for indoor gas build-up.

One 2017 study measured the effectiveness of five plant species, including popular houseplants like the Golden Pothos and Ficus, in reducing indoor concentrations of ozone.4

The researchers found that the ozone removal effectiveness of these plants ranged from 0.9% to 9% according to a leaf surface area to room volume ratio of 0.06 m-1. Taking this ratio and the cubic volume of air in a given room into account, the researchers suggest that you’d need one plant for every 1.8 square meters (just under 6 square feet) to remove, in some cases, less than 1% of the ozone from a room.

Think about that: to decrease even a fraction of the ozone in a 500 square-foot room, you’d need at least 80 plants. You might as well live in a jungle!

To decrease even a fraction of the ozone in a 500 square-foot room, you’d need at least 80 plants. You might as well live in a jungle!

So what’s the big deal about plants for purifying air?

Plants aren’t miraculous indoor air cleaners by any means, so why all the fuss about using plants to clean your indoor air?

In a 1989 report, NASA set off an entire generation of research into this topic. 

In the report, NASA detailed a study of 12 different plant species thought to be able to remove gas concentrations from enclosed, airtight spaces. At the time, NASA became concerned that a lack of fresh air exchange in space stations would allow gases to build up to dangerously high levels, and several plant species were proposed as a possible solution to this problem because of their phytoremediation properties.5

Preliminary results showed that the plants removed anywhere from 10 to 90 percent of these chemicals within a 24-hour period in a sealed environment filled with high amounts of the chemicals. But this study was not without several significant constraints:

  1. The test chambers in which the plants were placed were not constantly ventilated with air from outside the chamber.
  2. Each plant was potted in soil containing activated carbon, which is well known to absorb smoke, chemicals, bacteria and viruses (in fact, we use activated carbon filters in many of our purifiers, such as the GC™ MultiGas, for chemical filtration). The pots were then equipped with water and a small “squirrel cage” fan to take in air and feed it through the activated carbon soil. So the plants weren’t even filtering the ambient air itself - they were filtering already filtered air.
  3. The study only tested three volatile organic compounds (VOCs): benzene, trichloroethylene and formaldehyde.

More recently, a 2017 study built on NASA’s findings by using three types of Ficus plants:6

  • Rubber plants, which are used to make latex
  • Rhapis, a type of palm tree
  • Happy trees, a common indoor plant

Unlike the NASA study, this study was conducted on a building site rather than in a laboratory, and the researchers measured ambient concentrations of VOCs in a room in the building before, during and after putting plants in the building. The researchers also measured the levels of gases in a room in the same building without indoor plants to ensure that any noted gas reductions were indeed connected to the use of plants.

The researchers found that the three types of plants removed the following percentages of each of the studied VOCs from indoor air within a week:

  • Benzene: 9 percent
  • Formaldehyde: 50 percent
  • Ethylbenzene: 75 percent
  • Xylene: 72 percent
  • Styrene: 75 percent
  • Acetaldehyde: 36 percent
  • Acrolein with acetone: 35 percent
  • Toluene: 85 percent
In a typical building, it’s nearly impossible for even a large number of plants to keep up with VOC build-up.

The researchers claim that these percentages indicate the efficacy of these types of plants for purifying the air of VOCs, but the study fails to discuss the possible effects of human occupancy, off-gassing from appliances, and other factors that can regularly increase concentrations of VOCs in the environment. In a typical building, it would be nearly impossible for even a large number of indoor plants to keep up with VOC build-up.

So what do I do about my IAQ?

Researchers may disagree on just how effectively plants remove gas from indoor air, but the science indisputably shows that plants do nothing for particulate matter that may be floating around in high concentrations indoors, especially in newer homes that don’t get as much ventilation.

Harmful indoor particulate matter includes PM10, which encompassed larger particles like coarse dust, mold spores, and pollen, as well as PM2.5, which includes bacteria, viruses and ultrafine particles from vehicle exhaust that can easily get inside if your home or office is close to a busy street or a highway, even if the building is airtight.

Try the following to increase your awareness of indoor air pollution and empower yourself to do something about it:

  • Be aware of your Indoor Air Quality (IAQ). The first step in keeping your indoor air clean is using an air quality monitor knowing what’s in your air at all times. AirVisual Pro by IQAir uses cutting-edge laser technology to give you real-time measurements of six key pollutants, including CO2 and PM. AirVisual Pro also displays 72-hour historical and forecast data so that you can know exactly when and why your indoor air quality changes, whether it’s because of your indoor habits or factors in the environment.
  • Use an air purifier with HyperHEPA technology. Even more powerful than a typical HEPA air purifier, the IQAir HealthPro Plus® removes up to 99.5% of particulates down to 0.003 microns, which includes even the smallest pollutant particles like viruses and ultrafine particles from vehicle exhaust. The Atem®personal air purifier can also provide pure, pollutant-free air directly into your personal breathing zone.
  • Use advanced gas-phase filtration.
    • The HealthPro® Plus features our patented V-5 Cell gas and odor filter, designed to eliminate VOCs and other harmful chemicals using five pounds of activated carbon.
    • The GC MultiGas takes gas and odor filtration to the next level, featuring four cylindrical housings containing 12 pounds of activated carbon and impregnated alumina.The GC™ MultiGas is your best bet if indoor gases and chemicals are your biggest concern, providing almost three times as much activated carbon filtration as the HealthPro Plus in addition to our powerful HyperHEPA particle filtration.
  • Limit activities that introduce chemicals into your indoor air. Indoor plants may help clean chemicals that build up from off-gassing and other natural processes, but it can also help to stop doing things that bring even more chemicals indoors. 
    • Use green-cleaning chemicals that use less formaldehyde than regular cleaners.
    • Don’t burn wood or other solid fuels inside. Use a wood stove with a HEPA filter whenever possible.
    • Use a stove hood when you cook and regularly ventilate your home or building after cooking or cleaning, which can make indoor pollutant levels quickly spike to toxic levels.

Using plants will do little to clean your indoor air, while changing your indoor habits can drastically improve your IAQ. With newer, energy-efficient homes and buildings circulating less fresh air, making informed, intelligent decisions about your indoor lifestyle is an increasingly important part of making sure you’re always breathing the cleanest possible air.

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FOOTNOTES

[1] Gawronska H, et al. (2015). Phytoremediation of particulate matter from indoor air by Chlorophytum comosum L. plants.
DOI: 10.1007/s11869-014-0285-4

[2] Koenig, JQ. (2000). Health effects of ambient air pollution: How safe is the air we breathe? New York City, NY: Springer.

[3] Yang H, et al. (2011). Phytoremediation on air pollution.
DOI: 10.5772/19942.

[4] Abbass OA, et al. (2017). Effectiveness of indoor plants for passive removal of indoor ozone.
DOI: 10.1016/j.buildenv.2017.04.007

[5] Wolverton BC et al. (1989). Interior landscape plants for indoor air pollution abatement.
https://ntrs.nasa.gov/search.jsp?R=19930073077

[6] Hong S, et al. (2017). Study of the removal difference in indoor particulate matter and volatile organic compounds through the application of plants.
DOI: 10.5620/eht.e2017006

Air Quality Life is brought to you by The IQAir Group, the world’s leading innovator of Indoor Air Quality solutions since 1963. This online publication is designed to educate and inform the public about the latest research and news affecting indoor and outdoor air quality.

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