Expert Advice on Green Buildings

VOC Removal: Five Plants That Clean the Air and Remove VOCs

 

The U.S. Environmental Protection Agency (EPA) estimates that indoor pollution and/or contaminant levels may be two to five times (and potentially up to one hundred times) greater than outdoor levels. Potential threats to indoor environmental quality include the presence of hazardous chemicals, high concentrations of airborne fibers, and smoke, mildew, mold and/or fungus contamination.

VOCs are emitted from a wide range of consumer and commercially focused products. Such products include paints, carpets, furniture, pesticides, cleaning supplies, adhesives, sealants and coatings, copy paper and common office equipment, such as copiers and printers.

VOCs are released as gases from these products and may or may not always be noticeable, but they're there nonetheless. Indeed, that "new car smell" many people refer to is actually comprised of VOCs being emitted from the various new components, adhesives, paints, etc. in your car. VOCs include a variety of chemicals such as benzene, xylene, heptane, octane and others that may be hazardous to human health, especially indoors where large concentrations of VOCs may be present.

LEED and Indoor Air Quality

LEED's Indoor Environmental Quality category is entirely focused on indoor air quality and human productivity. LEED addresses indoor air quality in a variety of ways from encouraging new buildings to use low or no VOC materials and compliance with ASHRAE 62.1, to fresh air circulation and indoor air flushing. But there are simpler, less mechanical (and more beautiful) solutions for improving the quality of the oxygen we breathe and the productivity of the environment we work and live in.

Plants that Remove Volatile organic compounds

Plants are important elements of the human world. Indoor plants convert carbon dioxide to oxygen, essentially scrubbing the air we breathe while removing dangerous toxins.

A study by the University of Georgia published in HortScience conducted tests of ornamental plants' ability to remove harmful VOCs from indoor air, a process called phytoremediation. The effect of these plants on removing VOCs not only improved air quality, but also human psychological health.

According to the study, which tested twenty eight (28) different species of indoor plant, five (5) plants came out on top in terms of their ability to remove VOCs:

  • Purple Waffle Plant (Hemigraphis alternata)
  • English Ivy (Hedera helix)
  • Variegated Wax Plant (Hoya carnosa)
  • Asparagus Fern (Asparagus densiflorus)
  • Purple Heart Plant (Tradescantia pallida)

All of the aforementioned plants were were rated as superior in their ability to remove VOCs as well as provide incremental health benefits to building occupants.

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Expert Advice and Comments

Plants remove VOCs, and other dangerous beliefs

In fact, other than the transformation of carbon dioxide, primarily from human metabolism, the ability of plants to remove gases (such as VOCs) from indoor air is extremely limited. Contrary to the aggressive marketing by consultants and industries who provide advice on or actually provide the plants themselves for interior landscaping, the removal rates are so small that even the most energy-conserving building removes pollutants faster through unintended leakage -- around 1/10th of an air change per hour.

For plants to actually achieve the removal rates reported by some very old, oft-cited NASA research, you would have to fill a house with three layers of plants (floor-to-ceiling). There would be no room for the occupants. Studies in buildings where plants' ability to remove pollutants has actually been measured show that the effect is negligible. (References to some useful articles are provided at the end of this comment.)

1. Freeman correctly identifies mold as being among the hazardous pollutants in indoor air. Unfortunately, indoor plants do not remove mold. In fact, they have repeatedly been identified by researchers with higher levels of mold and fungal spores indoors. They are also associated with higher moisture levels which also result in a greater likelihood of mold growth. Plants take the moisture out of the growing medium and ultimately release most of it into the air as part of what is known as transpiration. (See the article "The Water Cycle: Transpiration" on the USGS web site at
http://ga.water.usgs.gov/edu/watercycletranspiration.html)

2. Freeman tells us that the new car smell is from VOCs and he names many sources but misses the main source of the new car smell, the plasticizers in the plastics that often cover seats, dashboards, kick panels, and roof liners in cars. Plasticizers are not VOCs, they are semi-volatile compounds which is why the smell lasts so long in a new car. If they were VOCs it would be easier to get rid of them.

3. We are told that there are simpler "solutions for improving the quality of the oxygen we breathe..." Actually, oxygen is an atom and we breathe it in the form of two oxygen atoms joined, or O2. It is not possible to improve "the quality of oxygen." The air we breathe is approximately 22% oxygen and 78% nitrogen with very small percentages of other gases and with particles including both viable and non-viable bioaerosols as well as particles combustion sources such as cooking, water heating, tobacco smoking, or wood-burning.

4. For more information, see articles posted on the web site http://BuildingEcology.com.

IAQ and Plants available at
http://www.buildingecology.com/articles/iaq-and-plants

Can house plants solve IAQ problems? at
http://www.buildingecology.com/articles/can-house-plants-solve-iaq-probl...

and Critical Review: How Well Do House Plants Perform as Indoor Air Cleaners? at
http://www.buildingecology.com/articles/critical-review-how-well-do-hous...