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Air Cleaning Plants & The Modern Office

“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)

We spend an estimated 90% of our time indoors, much of it stuck in the office

But the air quality of public buildings, especially modern offices can be very poor. This can 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. An old idea, but at the same time a relatively new one. This is because science is slowly offering evidence of the potential health benefits.

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

Yawning, tired worker stretching at their desk

Unsurprisingly, clerical workers who spend long hours at their desk are the most seriously affected by poor indoor air quality. This can lead to increased stress, diminished health and (inevitably) absenteeism.

Slowly but surely, employers are waking up to the impact this is having on their employees and consequently their business. The US Environmental Protection Agency even have a  section of their website for employers and employees understand the issue better.

Sick Building Syndrome

If poor air quality was not enough of a worry, 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 as they are products of modern office life.

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, paints, printers and other common features of modern offices.

These problems are magnified in modern buildings, where air-tight insulation prevents essential air circulation.

With this in mind, it is no wonder that people are interested in simple solutions that will improve indoor air quality. And plants, nature’s own air-recycling specialists, sit at the top of many lists.

The NASA clean air study

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

NASA were interested in the possible benefits of air cleaning plants because astronauts were being exposed to astronomical (!) amounts of VOCs. A combination of modern equipment and prolonged periods in airtight spaces was taking its toll.

An earlier NASA study had suggested that common house plants may offer a solution. So, NASA scientist Dr B.C Wolverton led a thorough study into how effectively plants remove airborne pollutants. The study conclusively proved that, in the right conditions, certain plants really did clean the air. What’s more, the effects could be measured.

Importantly, for the wider public, a number of the volatile organic compounds tested were the same ones commonly found in modern buildings. This included  benzene, formaldehyde and trichloroethylene, which would later be linked to ‘sick building syndrome’.

A trip to the nursery

The study was primarily concerned with finding out which plants made the biggest difference. Houseplants were chosen because of their ability to survive indoors.

After casually picking up a range of popular houseplants at the local nursery, they were placed inside sealed chambers. A measured dose of individual VOCs was then injected into the chamber. The level of VOC density was then measured at regular intervals over a 24-hour period.

The results were remarkable, as the graphics on the right illustrate [click the images for a larger view]. Over time, this study became widely known and opened up interest in the potential health benefits of office plants.

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

Concerns about the NASA clean air study

Now, before you rush down your local nursery to stock up on houseplants, there are more than a few caveats. Reasons that go a long way to explaining why offices did not suddenly transform into mini botanical gardens.

Perhaps one of the most important reasons was that, at the time, very little was understood about VOCs and indoor air quality. Perhaps more importantly, there was a recognition that offices were very different environments to NASA laboratories. While the results of the study itself were not disputed, there were several questions about how relevant the findings were modern office buildings.

  • Do air cleaning plants perform the same outside laboratory conditions? 
  • How many plants are required to make a positive difference to the wellbeing of my office workers? 
  • VOC dosage levels in the NASA study were extremely high. Although this was by design, so the results could be more readily measured, the levels were far higher than those found in offices.

Considering plants require ongoing care and attention, employers needed a more convincing case before investing in plants for anything other than decorative reasons.

Higher up the agenda were more proven methods to improve air quality. For example, steps could be taken to actively reduce the presence of volatile organic compounds and recycle the air more effectively.

Over time though, it became clear the NASA clean air study laid the groundwork for later studies that would look at the potential benefits of air cleaning plants in modern buildings.

Recent research into air cleaning plants

More recent studies into air cleaning plants have focused on how plants perform in the real world, far away from 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 ‘sick building syndrome’.

These are just of couple of examples of research on the subject. Other studies have looked at the impact of houseplants on air quality in other public environments, such as schools and hospitals. And a focus for some studies has been how much plants can help asthma sufferers. Many of these studies support the findings from the 1989 NASA study, although the outcomes can vary.

Studies can only go so far

As we’ve already noted, some of the misgivings about the potential of air cleaning plants is whether their effectiveness can be replicated in everyday working environments.

As such, it’s worth seeing the idea put into practice. Nowhere has attempted this on quite the scale seen in the Paharpur Business Center in Delhi, India.

As an office in the centre of Delhi, exposed to high levels of pollution, the workers had long suffered with poor air quality. But the boss was determined to do something about it.

His solution? Place around 1,200 plants with proven air-cleaning credentials around the office building.

The office employed over 300 people and, within 15 years, the building was 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, if you’re an employer you might still need some convincing. Some of the more obvious concerns include:

  • The need to care for them constantly
  • The possibility of mould and other allergy problems for staff
  • The fact plants can have both a positive and negative impact on indoor humidity
  • The space they occupy
  • 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 jungle than a working office.

But all this brings us back to the main question which some would argue is, at best, unanswered.

Do air cleaning plants make a real difference to the health of office workers

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 the air cleaning benefits of houseplants is minimal.

And some studies even conclude that certain houseplants may actually generate VOCs.

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 questions. But in the meantime, there are other reasons why office plants may be worth considering…

Do office plants boost creativity & productivity?

If the 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. This is relevant as one of the main ways that office workers chose to personalize their workplace was by adding more plants. This study produced eye-popping performance improvements. Results that both employer and employee should welcome:

Wellbeing 47%
Creativity 45%
Productivity 38%

This study expanded upon earlier studies which had already explored the positive effects plants can have on 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 related studies in the field, ‘What Are the Benefits of Plants Indoors and Why Do We Respond Positively to Them?’, is particularly informative.

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 is enough to reduce stress and improve patient wellbeing.

Plants and workplace personalization

It’s fair to note that some of these studies make the wider point that the key is to give office workers some choices in how their working environment looks.

This links to another school of thought that offering people the opportunity to personalize their workspace will make workers happier. We explore the importance of personalizing workspaces in more detail here.

But it does underline that office plants can do more than just clean the air and improve the health of office workers. They can also lift working spirits and provide real benefits for employers and employees.

Choosing the right plant for your office

Hopefully, this article has got you thinking. If so, you may be wondering what plants should you get for your workspace?

We should first note that it is likely that all plants clean ‘dirty’ air to varying degrees. However, only a handful have actually been tested.

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

Plus, those who’ve digested the studies would observe that different plants removed different levels of volatile organic compounds. There were very few proven to remove a wide range of airborne pollutants.

Because of this, experts recommend a variety of air cleaning plants 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 provided consulting services on how to improve indoor air quality. He recommends the following:

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

And if you’re wondering which air cleaning plants are best for your office, here’s 5 to get you started. These are all low maintenance plants with proven air-purifying credentials that will also look good in any 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 ideal plant for your office. We’ve included practical info about choosing and caring for your plant, plus useful info about their air-cleaning qualities. 

#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 air cleaning 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

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