Wolverton Environmental Services, Inc.


Indoor Air Pollution














      In the midst of the energy crisis of the 1970s, those in the building industry placed a high priority on energy consumption and conservation.  As a result, both old and new buildings were made more energy efficient.  Coinciding with these measures, came a change in the use of natural building materials and furnishings to a more widespread use of synthetic materials.  While a tightly sealed building is more energy efficient, it quickly became apparent that trapped within these structures were a mix of emissions of volatile organic chemicals (VOCs) from chemically formulated personal care products, carpeting, fabrics, pesticides, business machines, bioeffluents (emitted in the human breathing process) and airborne microbes.  All of these factors teamed together to create a chemical pea soup and resultant complaints of poor indoor air quality (IAQ).

     Only recently have many physicians begun to associate the increase in respiratory problems with exposure to poor indoor air quality.  Once the correlation was accepted, litigation began to wind its way through the courts against building owners, architects and others in the building industry.  As a result, insurance companies have paid millions of dollars in damages.   However, little progress has been made in mitigating the causes of poor indoor air quality.

Sources of Chemical Emissions can be found in the following chart.

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Current IAQ Methods

            The building industry has struggled with indoor air quality problems since buildings were made more energy-efficient.  After almost 30 years of only limited success, the building industry's primary form of remediation is increased ventilation rates.  Inherent problems with increased ventilation are: (1) reduced energy-efficiency (2) an assumption of clean outside air and (3) increased vulnerability to bio-terrorism.  Only recently have we begun to realize the added risk posed by increased ventilation.  Even a small amount of highly pathogenic microbes and/or toxic chemical agents introduced into air intake ducts could quickly contaminate large portions of a building and its inhabitants.   The September 11, 2001 terrorist attack on the World Trade Center in New York City should have been a wakeup call for the building industry.  Adjacent buildings were saturated by dust and debris much of which was introduced through the ventilation system.   Currently, the rapidly spreading SARS virus is again exposing some of the possible vulnerabilities of building ventilation systems.

      The building industry must accept the need to internally purify, revitalize and recycle air.  This is important for energy savings and to reduce the vulnerability of indoor air to biological and/or chemical agents that could be present in the outdoor air.

NASA and Indoor Air Pollution

     In 1973 during the Skylab III mission, NASA identified 107 volatile organic chemicals (VOCs) that were emitting (offgassing) from synthetic materials inside the spacecraft.  As a result, NASA realized that indoor air pollution in any tightly sealed structure could present health-related problems and should be addressed.  In 1989 EPA reported to the U.S. Congress that they had detected more than 900 VOCs in the air of public buildings.

     As part of its research into "closed ecological life support systems,"  NASA began to study the cleansing powers of nature through the synergestic reactions taking place between plants and their root microbes.  In 1984 NASA first published studies demonstrating that interior plants could remove VOCs from sealed test chambers.  In a progressive step up, NASA had constructed a tightly sealed building termed the "Biohome"   This structure was made with synthetic materials and engineered to achieve maximum air and energy closure.  The interior walls of the Biohome consisted of molded plastic panels with 30-cm of fiberglass insulation providing a thermal insulation value of R-40.  It was equipped to provide a fully functional habitat suitable for one person.   The remainder of the interior space housed a network of bioregenerative components using plants whose basic end products were reclaimed wastewater, potable water and purified air.  While the Biohome was not a completely closed system, many valuable lessons were learned.

     The Biohome was equipped with monitoring ports in each outside door for sampling air from inside this tightly sealed structure.  Before plants were added, mass spectrometer/gas chromatograph (mass spec/GC) analyses of the indoor air showed high levels of VOCs offgassing from interior synthetic materials.  Upon entering the building, one experienced severe burning of the eyes and respiratory discomfort, both classic symptoms of "sick building syndrome."

     Interior foliage plants were placed throughout the living quarters to evaluate their ability to remove VOCs outgassed from the newly constructed and furnished facility.  A small prototype fan-assisted plant filter was also placed in the living quarters.  This plant filter had the VOC removal capacity of 15 standard potted plants.  Air quality was again tested using mass spec/GC analyses.  Results showed that most of the VOCs had been removed.   The ultimate test was the fact that one no longer experienced the symptoms of "sick building syndrome."  This was the first "real world" application using interior plants to alleviate indoor air pollution. 

     It should be noted that the Biohome was a tightly-sealed, non-ventilated structure.  Highly ventilated buildings will overwhelm the VOC removal capabilities of interior plants or any other air filtration system.  In highly ventilated buildings, the VOC level indoors essentially equilibrates to the same level as the outdoors.

     As a case study, a student lived for one summer in the Biohome and did not have any IAQ complaints.  Waste recycling studies where the student's waste (cooking, bathroom, etc.) was treated and recycled within the wastewater treatment/food production section of the Biohome.  (See Figures 1 and 2.)

     After the research program concluded, NASA moved the Biohome to the Visitor's Center and renamed it 'One Mainstreet Mars.'  It continued its role as a valuable educational tool by simulating a life-support module on Mars, where the air and waste are treated by plants.  For many years, One Mainstreet Mars was one of the most popular exhibits for the young and old alike.  Unfortunately, it was destroyed on August 29, 2005 by Hurricane Katrina.


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Ecology Gardens

     Dr. Wolverton has served as a consultant to Takenaka Garden Afforestation, Inc., Tokyo's largest interior plantscape company for more than twelve years.  They have jointly conducted research into the use of plants to improve indoor air quality.  These studies have led to the development of 'Ecology Gardens' for use in public buildings.   Ecology Gardens are indoor gardens that use a specially formulated growth media containing in part a mixture of activated charcoal and inert materials.  Studies show that plants in Ecology Gardens are more effective in the removal of VOCs than indoor gardens in regular, commercially produced potting soil.  Ecology Gardens are now installed in seventy-one hospitals throughout Japan.  (See Fig. 3 - Tokyo Women's Medical College and Fig. 4 - Showa University Hospital.)  


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Figure 3


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Figure 4

For more information on Ecology Gardens, click on the following link:


See also their jointly authored new book, 'Plants: Why You Can't Live Without Them.'   

     Dr. Wolverton, in association with Takenaka Garden Afforestation, continues to research other methods to enhance the power of plants to create healthy indoor environments.  They anticipate the release of exciting new research results in the near future.


Plant Air Purifier

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     We now have more than twenty years of research proving the ability of interior plants to remove volatile organic chemicals (VOCs). The most recent use of the original NASA research is the development of a small, portable planter unit. The Plant Air Purifier® is manufactured and marketed by U. S. Health Equipment Company, Inc. located in Kingston, New York.

     This unit has advantages over the earlier models in that it has a much larger water reservoir and the container in which the plant is grown can be easily removed to replace plants. Earlier studies have shown that one plant in a small plant-based air filter can remove approximately the same amount of VOCs as 100 plants grown in non-aerated, commercial potting soil.

     The Plant Air Purifier® is an air filtration system that includes a planter, specially developed ceramic growing media, activated carbon and a low-voltage power supply. The planter itself consists of a perforated inner pot and a unique outer reservoir that holds enough water for up to one week or more, depending upon how often the fan is in operation. The planter has an electric fan to ventilate the system and a low-water switch in the water reservoir to turn off the fan when the water runs low. All that is required is a plant, periodic watering and a dose of nutrients every few months. Under normal conditions, the filter media never needs replacement.

The Plant Air Purifier® system pulls air down through the growing media where air pollutants are captured and held by the activated carbon until the microbes that populate the root system can utilize them as a food source. The activated carbon acts like a magnet to attract pollutants. The root microbes surrounding the carbon attach to the pollutants and breakdown and digest them. The resulting material becomes food for the plant roots to utilize.

For more information about the Plant Air Purifier®:

Plant Air Purifier® brochure: pdficon_large.png (1397 bytes)  Download Brochure

Plant Air Purifier® website: www.plantairpurifier.com


For More Information

See Reference page.

See also the NASA Technical Report Server.  This link provides technical reports written by Dr. B. C. Wolverton while employed with NASA at the John C. Stennis Space Center in Mississippi.  Click on the "NASA Technical Report Server" link above.  At the search window, type wolverton into the box to gain access to a number of reports (most are downloadable in PDF format).

     For more information see our Books page for information on how to order Dr. Wolverton's books.

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Contact Information

[601] 798-5875

Postal address
514 Pine Grove Road
Picayune, MS 39466-9042

Electronic mail

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