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“Indoor levels of pollutants may be two to five times — and occasionally more than 100 times — higher than outdoor levels”. The U.S. Environmental Protection Agency (EPA)

Indoor air quality

We spend an estimated 90% of our time indoors, much of it at work.

But the air quality of public buildings, especially modern offices can be very poor. In some cases, this may cause health problems for office workers, leading to absenteeism and reduced productivity.

There are a number of ways to address the problem, but one method that is gaining popularity is the use of air cleaning plants. You only have to view a selection of articles online to see how the idea has mushroomed.

But you may be wondering how much truth is there to the claims? In this article, we take an in-depth, balanced look at the research and insights shaping our understanding of indoor air quality and why plants may offer a solution.

Yawning, tired worker stretching at their deskUnsurprisingly, clerical workers who spend long hours at their desk are the most seriously affected by poor indoor air quality. This can cause stress, diminished health and lead to absenteeism.

This has become a growing concern for employers. The US Environmental Protection Agency even have a whole section of their website devoted to the problem of indoor air quality.

Sick Building Syndrome

If that is not enough, office workers also have to contend with ‘sick building syndrome‘ [SBS].

SBS symptoms include eye irritation, headaches, mental fatigue, lethargy, flu-like symptoms, as well as added complications for asthma sufferers.

A number of causes for SBS have been identified, although it is usually a combination of issues.  Some of the possible causes you might hear include:

  • Poor ventilation
  • Contaminants from outdoors
  • Toxins emitted by everyday office equipment
  • Noise issues
  • Bad lighting
  • Humidity
  • Poor ergonomic design
  • Biological contamination from stagnant water that has collected, whether in air ducts or other sources.

A few of these issues can be addressed directly, such as improving ventilation and cleaning procedures. But some are difficult to control.

One of the biggest problems is volatile organic compounds (VOCs). VOCs are found just about everywhere.  Although most are harmless, some are believed to have harmful long-term effects.

Many of the most unpleasant ones are generated by the office equipment and furnishings you use every day, including carpets and paints.

These problems they create are often magnified in modern buildings, where air-tight insulation restricts decent air circulation.

As you might expect, there is a lot of interest in simple solutions to improve indoor air quality. And plants, nature’s own air-recycling specialists, sit at the top of many lists. 

Can air cleaning plants fix things?

Air cleaning plants in a meeting room/officeYou may have heard some striking claims about the possible health benefits of air cleaning plants. Studies have shown that many popular houseplants remove airborne toxins. They can also improve humidity levels in dry, air-conditioned offices.

But you may not be aware that studies have also shown that office plants can help create a more productive and creative working environment. And a small, but growing, number of employers are waking up to the possible benefits for them and their workforce.

The NASA clean air study

Serious interest in how ordinary houseplants can improve air quality was sparked by a 1989 NASA clean air study.

Led by Dr B.C Wolverton, the study demonstrated that a wide variety of common houseplants can remove harmful airborne pollutants. Notably, this included benzene, formaldehyde and trichloroethylene. All commonly occurring volatile organic compounds associated with ‘sick building syndrome’.

The research expanded upon earlier research into air purifying plants for NASA which had shown promise. While offices may be home to many VOCs, this pales in comparison to the amount of VOCs astronauts are exposed to. As such, NASA had extra motivation to find solutions.

A trip to the nursery

To identify the most effective air cleaning plants, a variety of common household plants were casually picked up at the local nursery.

The plants were then placed inside sealed chambers.

A dose of measurable air pollutants was then injected into the chamber, including formaldehyde and benzene. VOC levels were them measured at regular intervals over a 24-hour period.

The results were striking, as the graphics on the right illustrate [click the images for a larger view].

If you like to really chew on the detail, you can read the full, NASA clean air study pdf here. There’s also more info on Dr Wolverton’s website  and details of related studies on the NASA site.

So popular were the findings, Dr Wolverton has also authored a couple of books, including one from 2010 titled “Plants: Why you can’t live without them”.

Detailed infographic showing the % removal of benzene with a variety of air cleaning plants

Concerns about the NASA clean air study

Although the results were striking, not a lot changed. Businesses did not embrace the findings, let alone act on them.

Not many businesses would have considered this a priority, regardless of its conclusions. An important consideration is that nobody had easily demonstrated that poor quality indoor air was causing measurable harm.

Even if you were sold on the idea that offices might not be great for your health, you would have found a number of important questions unanswered:

Will the plants perform the same outside laboratory conditions? 

How many plants are required to make a positive difference to the wellbeing of my office workers? 

Plus, the methodology might raise a few concerns. For example, the VOC dosage levels in the NASA study were extremely high, so the results could be more readily measured. And the measurements were taken from sealed containers. These 2 conditions did not reflect any office people actually worked in.

As plants are living organisms that require care and attention, investing in office plant were not top of the agenda.

Higher up the agenda were more proven methods to improve air quality. For example, you could take steps to reduce the presence of volatile organic compounds.

Or you could try to recycle the office air more effectively. Keeping the air-conditioning clean and efficient should also be a priority.

With hindsight, we can see the NASA clean air study was groundbreaking. But it was a few more years be its importance was realized, opening the door to research that sought to address the holes in the NASA study.

Recent research into plants that clean the air

More recent studies into air cleaning plants have focused on how plants perform in the real world, far away frrom a laboratory.

study by the University of Aveiro in Portugal [2011] measured air pollution in a school classroom before and after the addition of 6 hanging plants. This resulted in a 30% reduction of particulate matter, as well as reducing VOCs. In summarizing, the study stated that:

“Our findings corroborate the results of NASA studies suggesting that plants might improve indoor air and make interior breathing spaces healthier”.

An earlier report from the University of Technology, Sydney, had already assessed plants in both a controlled environment and in real life situations. This included ‘field studies’ in 60 offices.

The study concluded that potted plants can “reliably reduce total volatile organic compounds…by 75%”. The study also illustrated how indoor plants reduce carbon dioxide levels, which can also contribute to SBS symptoms.

While these studies are directly relevant to office workers, there have also been a number of other studies which support the case. 

Studies can only go so far

As we’ve already noted, some of the misgivings about these studies is whether they can be replicated in everyday working environments. 

For this, you should check out the office of Paharpur Business Center in Delhi, India.  The office had long suffered with poor air quality. But they were determined to do something about it. 

Their solution? Introducing around 1,200 noted air cleaning plants throughout the building. 

The office employed over 300 people and, just 15 years later, the building is recognized as one of the healthiest in India. Staff there have reported significant reductions in eye irritation, respiratory conditions and headaches.

Air cleaning plants at the Paharpur Business Centre, Delhi. Home to 1200 plants & some of the cleanest air in Delhi.

Paharpur Business Centre, Delhi. Home to 1200 plants & some of the cleanest indoor air quality in Delhi.

So significant was the achievement, the man behind it all, Kamal Meattle, is often invited to talk on the subject. You can hear more from the man himself in this short TED talk

How many plants?

Even if you accept the science behind the claims, you might still remain unconvinced that plants are worth the investment. This if often due to simple practical concerns:

  • Constant care needs
  • The possibility of mold and other allergy problems for staff
  • Plants can have both a positive and negative impact on indoor humidity
  • Plus, they can attract bugs

There are ways around this problem, particularly through careful selection of low-maintenance plants.

But it’s reasonable to ask just how many plants does it take to improve air quality. After all, the acclaimed Delhi office has around 1,200 plants and looks more like a botanic garden than a working office.

But all this brings us to the main objection.

Do air cleaning plants make a genuine difference

The US Environmental Protection Agency says this on the subject:

 “There is currently no evidence… that a reasonable number of houseplants remove significant quantities of pollutants in homes and offices”.  

And the US EPA are not alone. A 2014 review of the available, relevant studies also arrived at the same conclusion. That review concluded that studies conducted in real-life settings such as offices and homes are few and show mixed results.” Hardly a ringing endorsement. 

This followed an earlier 2009 study that concluded:

“A careful examination of studies does not find convincing evidence that the use of plants indoors can result in meaningful reductions in indoor VOC concentrations”.

On top of this are studies showing that certain houseplants may actually generate VOCs. Or rather the pesticides they were treated with, as well as the plastic pots and soil they were sold in.  Included in the study were plants that featured prominently as air cleaning plants in the NASA study, including Peace Lily and Weeping Fig.

Confused? Clearly the case is not clear-cut, but there’s plenty of food for thought. In the future, hopefully we will see more conclusive studies that resolves some of the big questionmarks.  

Do office plants boost creativity & productivity?

If the mere possibility of breathing cleaner air is not enough to inspire a trip to the local nursery, what about the claim that indoor plants can also boost productivity and creativity?

A 2014 study by several British universities boldly suggested that enriching an office with plants “could increase productivity by 15%.

Further research from the University of Exeter (UK) showed that even bigger improvements were found when staff were invited to personalize their workplace. The more personalized workspaces tended to have more plants and art.  Although this study was not just about air cleaning plants, its results are worth noting. Eye-popping results, for employer and employee alike:

  • Wellbeing...47%
  • Creativity...45%
  • Productivity...38%

A much earlier study had already explored the positive effects plants can have on employee productivity, albeit with less striking results. A 1996 study from Washington State University showed that:

“Productivity increased 12 percent when people performed a simple task on a computer in a room with plants compared with workers who performed the same task in the same room without plants.”

Virginia I Lohr, the author of the 1996 study has carried out further research in the field. Her 2010 review of other related studies in the field is particularly informative. What Are the Benefits of Plants Indoors and Why Do We Respond Positively to Them?“.

Supporting this is a 2007 study from the University of Twente (Netherlands). Although this study was conducted in hospitals, it demonstrated that the aesthetic appeal of plants alone is enough to reduce stress and improve patient wellbeing.

Plants and workplace personalization

Some of these studies made the wider observation that granting office workers some choices in how their working environment looked may be a major factor in the improvements recorded.

This links to another school of thought that offering people the opportunity to personalize their workspace makes for happier workers. We explore that in more detail here.

But it does underline that if you are simply allowed to have a plant or other cherished objects on your desk, it may make your happier. And even the most tyrannical employer would welcome the boost in productivity and creativity. We hope…

Choosing the right plant for your office

Hopefully, this article has got you thinking. You may even be wondering what plant should you get for your workspace?

It’s likely that all plants clean ‘dirty’ air to varying degrees. However, only a handful have proven their capabilities in scientific studies.

There are, for example, over 850 species of Ficus tree and only one that features prominently in most studies, Benjamina Ficus.

If you’re in the position to add more than a desk plant, don’t forget that the NASA study clearly showed that different plants removed varying levels of volatile organic compounds. Ideally, you would have a mix of different plants that are known to tackle a broad spectrum of VOCs and other harmful pollutants.

If you’re wondering how many you should start with, you could do worse than follow Dr Wolverton’s advice. The author of the original NASA study now runs a business that consults on how to improve indoor air quality. He recommends the following:

2 Good sized plants per 100 sq. feet [9.29 sq. meters]

And if you’re wondering which plants, here’s 5 to get you started. low maintenance plants that will clean your office air and enrich your workspace.

Office environments are far from ideal for every plant species. If you want a plant that will thrive in your workspace, check out our guide to choosing the right plants for your office. We’ve included practical info about choosing and caring for your plant, plus all their air-purifying credentials. 

#Peace Lily [Spathiphyllum]

 VOC Removal: benzene, formaldehyde, trichloroethylene, toluene, xylene & ammonia! Quite the performer…               

 Easy to care for and adapts to low light well. Produces beautiful lasting blooms for even the most brown-thumb owners 

  Unpleasant if swallowed by children.

Toxic for pets.

Peace Lily in white vase

#2 Areca Palm [Dypsis lutescens]

 VOC Removal: Xylene & Toluene                           

Moderate care required – ideal for office corners or desktops if regularly pruned. Prefers indirect sunlight. 

Not considered toxic

Potted Areca Palm

#3 Golden Pothos, aka ‘Money Plant’, ‘Devil’s Ivy’ [Epipremnum aureum]

Air cleaning plants iconVOC removal: Another stand-out performer from those famous NASA studies, proven to reduce levels of formaldehyde, acetone and xylene               

   This one if famously low maintenance. You’ll also find it is low-light tolerant and very hardy. However, you may need to prune it from time to time to keep your desk from becoming a jungle. 

Toxic for humans & pets

Golden Pothos - Devil's Ivy

#4 Spider Plant [Chlorophytum comosum]

Air cleaning plants iconVOC removal: Formaldehyde, xylene & toluene  

You’ll find this very easy to care for and forgiving of many mistakes. Great if you have a window desk, as it won’t mind a bit filtered sunglight. Can produce ‘spiderettes’ which you can pot for new plants.                         

Hallucinogenic if ingested by cats (although not toxic for either cats or dogs)

#5 Chinese Evergreen [Aglaonema]

Air cleaning plants iconVOC Removal: Found to remove both formaldehyde and benzene in early NASA tests. These plants can last years if you look after them. Reportedly, more mature plants are even more effective at removing airborne pollutants

Perfect if you’re looking for an easy to care plantknown for it’s hardiness. Low light tolerant and ideally suited to just about any desk                 

Toxic for pets

Chinese Evergreen - Aglaonema

Smiling emojiSmiling emojiThanks for reading. We hope you find something of interest!

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