Wolverton's Clean Air Studies

by Joelle Steele

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As early as 1970, scientists and the general public were fast becoming aware of the fact that our indoor air was often very heavily polluted by common everyday substances that contained chemicals emitted into the air we breathe.


Among the many pollutants of our indoor air are these most toxic substances:

Methylene chloride. Found in paint strippers, adhesive removers, and aerosol paints, this chemical is known to cause cancer in animals and converts to carbon monoxide in the body, where it can cause symptoms associated with exposure to carbon monoxide.

Benzene. Found in gasoline, inks, oils, paints, plastics, rubber, tobacco smoke, and auto emissions, it is a known human carcinogen and irritates the skin and eyes. Chronic exposure at low levels can cause headaches, appetite loss, drowsiness, nervousness, psychological disturbances, and blood diseases, including anemia and bone marrow disease.

Perchloroethylene. This chemical, most widely used in dry cleaning, has been shown to cause cancer in animals. Studies indicate that people breathe in low levels in homes where dry-cleaned goods are stored and as they wear clothing that has been dry-cleaned.

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Trichlorethylene. This product is also used in dry cleaning, as well as in metal degreasing. It is found in printing inks, paints, lacquers, varnishes, and adhesives. The National Cancer Institute considers it a potent liver carcinogen.

Formaldehyde. Found in almost all indoor environments, its major sources are urea-formaldehyde foam insulation, particle board and pressed wood products, grocery bags, waxed papers, facial tissue, and paper towels, cigarette smoke, and heating and cooking fuels such as natural gas and kerosene. It irritates the mucous membranes of the eyes, nose, and throat, and the disease most often attributed to it is asthma.


Dr. Bill Wolverton spent 18 years as a research scientist working for the National Aeronautics and Space Administration (NASA) at the John C. Stennis Space Center in Mississippi. In 1973, NASA found that the air inside Sky Lab 3 was contaminated with more than 100 chemicals, and Wolverton was asked to find a solution. This was at a time when the issue of indoor air pollution was being discussed in the press where it was labeled "sick building syndrome," a collection of symptoms characterized by flu-like illness, mental confusion, memory problems, depression, headaches and other symptoms.

Wolverton began his clean air studies by theorizing that house plants could remove substantial amounts of benzene, trichlorethylene, and formaldehyde, as well as other chemicals such as nitrogen dioxide, from the air during the plants' natural processes of photosynthesis and respiration. To test his theories, Wolverton potted plants in carbon filters inside sealed chambers, and then introduced benzene, formaldehyde, and trichlorethylene into the chambers. Within a 24-hour period he noted the following:

Formaldehyde was decreased:
90 percent by Aloe vera
86 percent by Chlorophytum elatum ("spider plant")
86 percent by Philodendron domesticum ("elephant ear philodendron")
76 percent by Philodendron selloum ("lacy tree philodendron")
71 percent by Philodendron oxycardium ("heart leaf philodendron")
70 percent by Dracaena massangeana ("corn plant")
67 percent by Epipremnum aureum ("golden pothos")
67 percent by Syngonium podophyllum ("arrowhead plant")
61 percent by Chrysanthemum morifolium
60 percent by Dracaena marginata ("dragon tree")
50 percent by Gerbera jamesonii ("African daisy")
50 percent by Spathiphyllum `Mauna Loa' ("peace lily")
50 percent by Dracaena deremensis 'Warneckii' ("ribbon plant")
47 percent by Ficus benjamina ("weeping fig")
47 percent by Peperomia obtusifolia
41 percent by Brassaia arboricola ("umbrella tree")
33 percent by potting soil

Benzene was decreased:
90 percent by Hedera helix ("English ivy")
80 percent by Spathiphyllum 'Mauna Loa'
79 percent by Dracaena marginata
78 percent by Dracaena deremensis 'Janet Craigii' ("craigii")
73 percent by Epipremnum aureum
70 percent by Dracaena deremensis 'Warneckii'
68 percent by Gerbera jamesonii
54 percent by Chrysanthemum morifolium
53 percent by Sansevieria laurentii ("snake plant")
48 percent by Aglaonema modestum ("Chinese evergreen")
20 percent by potting soil

Trichlorethylene was decreased:
50 percent by Spathiphyllum 'Mauna Loa'
41 percent by Chrysanthemum morifolium
24 percent by Dracaena deremensis 'Warneckii'
18 percent by Dracaena deremensis 'Janet Craig'
13 percent by Dracaena marginata
13 percent by Sansevieria laurentii
11 percent by Hedera helix
9 percent by potting soil

Since formaldehyde is found in the highest concentrations indoors, Wolverton suggests that installing enough plants to remove the formaldehyde will automatically remove the other chemicals as well. He has since studied many other plants and their abilities to remove other toxic chemicals found in paints, carpet, linoleum, etc. He has found that it is not necessary for a room to be a jungle in order to clean the air; two sanseveirias could remove the pollutants in a 10' x 15' x 8' room. He suggested that one plant per 100 square feet was a suitable air purifier.


Because the EPA uses removal rates in micrograms, Wolverton decided that the percentages he released in his intial studies were not easily usable by consumers. So his data is now povided in micrograms per hour, which makes it possible to calculate the exact number of plants needed in any given room for effective air purification.

The following is a list of plants using Wolverton's more user-friendly method:

Dwarf date palm removes 610 micrograms per hour
Dieffenbachia removes 341 micrograms per hour
Dracaena marginata removes 338 micrograms per hour
Dracaena massangeana removes 274 micrograms per hour
Ficus benjamina removes 271 micrograms per hour
Spathiphylum removes 268 micrograms per hour
(other plants have been studied too with similar results)


Wolverton retired from NASA and for several years received all the funding for his clean air studies from the Plants for Clean Air Council. He also works with his research engineer/scientist son, John Wolverton, and he has also designed waste water purifications systems as a consulting environmental engineer. In 1991, one of these systems was being installed in the Math and Science building at Northeast Mississippi Community College in Booneville, Mississippi. Said Wolverton, these air and sewage treatment rooms are "built the way buildings should have been built in the first place." His air and waste water purifications systems using plants were implemented in the Arizona Biosphere 2, where plants were used as the primary means of life support and the sole source of cleaning the air and purifying waste water.

And Wolverton practices what he preaches in his own home in Picayune, Mississippin, where in 1989 he created a completely closed ecological life support system in which plants recycle wastewater and air through plant filtration systems. He also uses American chameleons to keep plant pests under control.


Wolverton's ongoing clean air studies include researching both soils and foliage for their respective effectiveness in reducing air pollutants, and determining what the plants are doing physiologically that allows them to filter chemicals from the air. He is studying the ability of plants to remove other chemicals, such as chloroform and xylene, from the air. And he is studying bioeffluence, the chemical pollutants such as methyl alcohol, aceton, and ethyl alcohol which are emitted by people in the process of breathing. He found that bioeffluence chemicals were easier to remove than other chemicals, and that a single spathiphyllum could remove aceton at a rate of 5,400 micrograms per hour, which is faster than the original emission rate of the chemical.


According to Wolverton, plants are the "lungs of the earth," and there is still a lot to learn about them. "Plants make for a better environment in ways we don't even know yet," he states. And the scientific community, skeptical at first, is now more accepting of his studies.

[Bill Wolverton completed his bachelor's degree in chemistry at Mississippi College. He completed three years of graduate study in medical microbiology at the University of Mississippi Medical School and earned his Ph.D. in environmental engineering at the Institute for Advanced Studies in St. Louis, Missouri. He provides consulting services to federal, state, and local agencies, to other countries, and to engineering firms and industrial manufacturers. He has authored more than 70 technical papers and has received many patents and awards, including the Federal Environmental Engineer of the Year Award in 1983 and one of the first five inductees into the U.S. Space Foundation's Space Technology Hall of Fame.]

This article last updated: 06/13/2012.