The scourge of gardeners, English Ivy — an invasive species — may be better than HEPA filters for indoor air quality
Modern heating, ventilation, and air conditioning (HVAC) systems attempt to replicate the cleansing air flows of the great outdoors but are limited by resource consumption and financial costs. Fortunately, we may overcome these limitations by introducing a freely available filtration supplement, Hedera helix L. (English Ivy), into our homes and offices.
The ongoing push toward energy efficiency and carbon footprint reduction commands constant advances in thermal insulation technology. Higher R-value construction materials reduce heat exchange and energy consumption, thereby decreasing carbon footprint. But enhanced thermal integrity also means moving buildings ever-closer to hermetically sealed chambers.
Modern construction attempt to address the lack of clean recirculated air by upgrading HVAC systems to high efficiency particulate air (HEPA) filtration. According to the American Society of Heating Refrigerating and Air Conditioning Engineers, these air cleaning systems must extract at least 99.97% of particulate matter 0.3 microns or greater in size. Unfortunately, this particulate extraction does nothing to purify the air of non-particulate matter such as volatile organic compounds (VOCs). HEPA and similar non-charcoal systems do not filter VOCs, thus spreading these potential carcinogens throughout the ventilated space.
VOCs commonly found in buildings include benzene, trichloroethylene, and formaldehyde. We may recall the air-quality concerns among FEMA trailer inhabitants displaced by Hurricane Katrina. Well, such compounds often originate from construction materials that off-gas from their sources into the surrounding environment. And while the green movement toward low or zero-VOC construction materials is a sound improvement, it does not prevent VOCs introduced by furnishings or appliances. A combination approach of prevention and treatment may be most realistic for combating recirculated air pollution.
Activated charcoal filters are commercially sold for air filtration of non-particulate matter, but can be costly and do not have the regulatory oversight of HEPA technology. Without agreed-upon performance standards, it can be difficult to assess the value of an activated charcoal air purifier system. Fortunately, a supplementary air purifier is freely available to inhabitants of the eastern and western US: English Ivy.
Introduced by English colonists in 1727, English Ivy rapidly adapted to the US and has become an invasive species. Anyone who has removed this ivy from a wall or tree understands the challenge of complete eradication. Thus, this weed’s resilient nature makes it a candidate for indoor cultivation. In 1989, the National Aeronautics and Space Administration (NASA) discovered it is also a candidate for indoor VOC filtration.
Through research intended to study plants as natural filters for space habitats, a NASA study determined that certain flora, and bacteria present in their soil, have higher VOC filtration rates than bare soil. From the published research, English Ivy is the most successful plant for filtration when equally weighting microgram extraction of benzene, trichloroethylene, and formaldehyde per cm2 of leaves. A further finding of this research is improved toxin filtration when maximizing plant root soil area. By trimming foliage in contact with the soil, plant roots and microorganisms can more efficiently biodegrade toxic chemicals from the air.
Of course there are caveats. While indoor VOC levels can vary from 2 to 5 times outdoor levels, not much is known about the concentrations of VOC pollution and adverse health effects. The minimum exposure levels necessary for a specific toxic effect are rarely known and minimum toxic dose estimates for a general population may overestimate the doses affecting sensitive individuals. Given the research at hand, what can we do to calculate the number of plants for reasonable filtration?
Assuming formaldehyde as a proxy for all VOCs, we infer that 1 m2 (assume 635 triangular leaves) of English Ivy should extract about 86,605 micrograms of pollution from 1 m3 of air in 24 hours. According to an NIH publication on toxic air pollutants, indoor formaldehyde levels have been recorded as high as 4,526 micrograms per m3. So if your well-sealed, highly polluted, office or bedroom were 28 m3 (10’ by 10’ by 10’), about 15 plants (940 leaves) should clean the air each day. That’s a lot of watering and frankly, you should move to a less contaminated building. Given this extreme example, a reasonable tradeoff for the space is 4 plants: require a quarter of the care and biodegrade up to 1,205 micrograms per m3 (27% of the highly polluted space). Remember that trimming the foliage in contact with the soil and strategic placement of these plants should optimize VOC biodegradation. For a rule of thumb, see the following formula:
Before going outside to ghost your yard of this pest consider that English Ivy is toxic if consumed by humans or pets. Be aware of the hazards English Ivy could pose and consider alternative plants researched in the NASA study. Also be aware that though plants like English Ivy can off-gas VOCs, the quantities are inconsequential (if using zero-VOC pots).
The benefits of a HEPA and activated charcoal air filtration systems come at high resource and financial costs. Relocating invasive plant species indoors can reduce these costs by providing supplemental non-particulate air filtration. And as will be evident in a future blog post, lower air exchange can at times, even reduce indoor air pollution.
Kevin Danielson is Senior Analyst within the Business Advisory Services Group at Altarum Institute, where he has developed and implemented a variety of consumer and market predictive models in the mortgage, commercial banking, small business, and health care industries.