Plants as a building service

Plants are proven to remove pollutants and improve air quality, but which species should be considered? Researchers from the University of Birmingham and the RHS review the latest research looking for answers

Posted in May 2019

Research suggests succulents such as Zamioculcas zamiifolia could be effectively used in indoor green walls

Research suggests succulents such as Zamioculcas zamiifolia could be effectively used in indoor green walls

Plants feature in many ways within indoor environments – from simple houseplants to complex, species-rich green walls – and they offer multifaceted services, including pollutant removal and reduction of building energy consumption.

This review identifies pollutants that have been measured at harmful concentrations indoors and gives health assessments of each. It explains which plants remove ‘2019’s priority pollutants’ effectively and directs research to those that have not been investigated. Finally, it consolidates the current research, presenting why plants should be considered a building service.

Plants deliver an array of benefits indoors, offering improvements in human health (pollutant removal) and in building energy consumption by the removal of carbon dioxide (CO2) and relative humidity (RH) regulation – which, in turn, reduces ventilation requirements (1, 2). 

Numerous airborne pollutants are present in indoor environments: these include volatile organic compounds (VOCs), inorganic gases/vapours (CO2, nitrogen dioxide – NO2) and particulate matter (PM) (3). The main sources of such pollutants are indoor human activities, construction materials, and the infiltration of outdoor-produced particles and pollutants. (4-6)

Activities such as cooking, cleaning and painting produce numerous indoor pollutants (6,7). In addition, the closure of windows – and a push for more tightly sealed buildings in an attempt to reduce energy consumption – leads to an accumulation of indoor pollutants (5, 8).

In western Europe people are commonly exposed to more than 20 hours per day of indoor air (9).Thus, quantifying the concentration of indoor pollutants with relevant safe exposure guidelines/standards is imperative – a guideline is based upon scientific evidence or expert opinion and a standard contains enforceable regulations adopted by regulatory authorities (10). Such health guidelines produced by organisations such as the World Health Organisation (WHO) and US Environmental Protection Agency (EPA) contain only a limited number of indoor pollutants (6, 11).

Indoor pollutants cause an array of acute and long-term (chronic) health problems, contribute to poor indoor air quality (IAQ) and are the probable cause of sick building syndrome (SBS), a phenomenon describing health issues experienced by the occupants of a building, caused by spending time within the building but, where no specific cause can be found (6, 12). Moreover, indoor pollutants also react with ozone and produce radicals and secondary organic aerosol (SOA) – both, considered harmful to health (13, 14).

Indoor pollutants vary in toxicity and prevalence. Prolonged exposure to an indoor pollutant, at a concentration greater than the recommended guideline, can cause symptoms such as mild sensory irritation (in the presence of alpha-pinene, for example) to significant respiratory problems (NO2) and cancer (benzene) (6, 15).

Indoor plants have been shown to remove a wide variety of organic and inorganic pollutants (1, 16), PM (17-19) and ozone (20, 21). Houseplants can also help alleviate the symptoms of sick building syndrome (SBS) (22-24).

High indoor concentrations of CO2 are harmful to human health, increase absenteeism and reduce cognitive performance (25-30), so HVAC systems are designed to keep concentrations low, with ventilation increasing energy consumption (31). Indoor plants can act as a simple, low-cost ventilation surrogate, contributing to CO2 removal indoors and reducing the requirement for traditional HVAC systems by about 6%.

Indoor plants can also reduce energy consumption by increasing RH. HVAC systems typically attempt to keep RH in the range of 40-60% – where the majority of adverse health effects can be avoided (32). A RH that is either too high (> 60%) or too low (< 40%) can cause health and building issues (32). High RH encourages fungal and mould growth, and contributes to the deterioration of building materials (33-36). Low RH can cause dryness of the eyes, skin and mucus membrane, enhance indoor ozone, increase the likelihood of influenza transmission, and exacerbate problems of static electricity (32, 33, 35, 37-39).

Our review aims to improve the current understanding of which indoor pollutants – and at what concentrations – are harmful to health.

A systematic review of the literature was conducted to determine the indoor pollutants measured in home environments, up to and including 2018.

Logue et al compared indoor pollutant concentrations with relevant health guidelines produced by the Environmental Protection Agency (EPA) and California Office of Environmental Health Hazard Assessment (OEHHA) for 67 home environments between 1998 and 2010. They identified nine ‘priority’ indoor pollutants (see Figure 1, which does not include butadiene) considered to be harmful. (40) All were chosen on the basis of the measured concentration data exceeding health guidelines and the number of homes affected.

Since 2010, an assessment of ‘Logue’s priority pollutants’ and their mean concentrations in indoor environments has not been carried out. So we have used data from home environments after 2011 to determine if concentrations of these nine pollutants have changed since.

Furthermore, we compare the post-2011 results with up-to-date chronic health guidelines produced by the World Health Organization (WHO) and US EPA (Figure 1). Any pollutants with an average long-term concentration greater than the appropriate guideline will be designated a ‘2019 priority pollutant’.

The data collected in Figure 1 suggests that the mean concentrations of four indoor pollutants have increased in studies after 2010 – namely, benzene, naphthalene, NO2 and PM2.5. Reductions in concentrations of acetaldehyde, acrolein, dichlorobenzene – 1,4 and formaldehyde were measured, perhaps because of a large body of research focusing on lowering pollutant emissions from building materials (52-54).

Acetaldehyde, benzene, formaldehyde, and NO2 are the indoor pollutants commonly measured at concentrations greater than the appropriate guidelines (Figure 1) – causing long-term health issues and, thus, being classified as 2019’s priority pollutants.

Indoor plants

Forty studies have investigated numerous indoor plants for their ability to remove the ‘2019 priority pollutants’ benzene (> 45 species/cultivars) and formaldehyde (> 150 species/cultivars). The results from the most robust, well-cited and informative studies from these have been selected and are presented in Table 2.

To the author’s knowledge, no studies have investigated the potential of indoor plants to sequester either acetaldehyde or NO2 – although the removal of NO2 by outdoor plants has been thoroughly studied, with promising results (71, 72).

Plants as a building service

CO2 removal

The main sources of CO2 indoors are human respiratory emissions and the outdoor air-supply rate. Several health guidelines exist for maximum safe CO2 concentrations, with the lowest eight-hour guideline being recommended by ASHRAE, at 1,000ppm. (1,77)

A number of studies have focused on indoor plants and their ability to reduce CO2 concentrations, with several focusing on houseplants specifically. Studies vary in scale and focus, but most use experimental chambers enclosing a single or small number of houseplant species.

Studies generally find that significant reductions can occur with the correct environmental conditions: namely, the light level. We found that raising the light level to 22,000 lux – made achievable with supplementary LED lighting – increased the CO2 removal 50-fold in some species.

Moreover, we estimated that 15 spathiphyllum wallisii verdi – a number that could, realistically, be installed in a small green wall – could offset 10% of a human’s respiratory contribution. A similar study by Torpy et al found that a 5m2 green wall containing chlorophytum comosum could balance the respiratory emissions of a full-time occupant using a similar lighting level.

RH regulation

Along with high CO2 concentrations in indoor environments, an additional challenge is extreme RH (low < 40% and high > 60%). Both can cause previously described issues, mainly concerning human and building health. Several studies have investigated the effect of indoor plants on RH, with mixed results. Indoor plants have been shown to increase, decrease and have no statistically significant effect on RH indoors. Houseplants release water vapour into an environment through transpiration and would be expected to increase RH indoors.

Plant-species choice and ventilation rate would both significantly influence results, and most likely explain the mixed results in literature. However, correct employment of indoor plants, with species consideration, could help reduce the energy consumption of HVAC systems.

Our research suggests that less physiologically active plants – such as Guzmania sp, dracaena fragrans and succulents such as zamioculcas zamiifolia – could be used in larger numbers (10+), as part of indoor living walls within even smaller offices, without a risk of raising office RH above 60%.

Conversely, hedera helix (ivy) and spathiphyllum (peace lily) would be suitable in smaller numbers (five or fewer), or in larger rooms with greater overall volume, where their RH-influencing effect would be diluted.

Conclusions

A significant body of research has looked at the ability of plants to remove indoor pollutants such as VOCs. Most, however, focus on pollutants that are detected infrequently indoors or at concentrations too low to damage human health. Experiments also commonly test pollutant concentrations that are not measured in real life (in situ).

This review highlights the range of concentrations present in situ and which indoor pollutants can be considered unsafe, to help direct future research.

Experiments suggest that the growing substrate, and the microorganisms within, are predominately involved in the removal of pollutants; plants themselves are only used indirectly to maintain and support substrate microorganisms.

Results generally suggest that the plant-substrate system can remove a wide variety of pollutants, but – with a lack of testing at in situ concentrations – extrapolation of the results to room level lacks accuracy. Further experiments should focus on the untested 2019 priority pollutants identified in this review, acetaldehyde and NO2 – preferably at in situ concentrations.

Certain houseplants can remove CO2 at significant quantities that would affect room-level concentrations, but only with the correct environmental conditions – for example, light level. Studies often suggest that a greater number of potted plants than would be feasible indoors (1, 2, 83) are required to measure concentration reductions, so the density provided by green walls would be more suitable.

Studies are now beginning to investigate green walls (77) and, additionally, how the substrate may influence removal – as measured with VOCs. RH literature has produced conflicting results.

Anecdotally, plants would be expected to increase RH indoors (2, 85, 86) , but this is not always the case (24, 84). We suggest a ‘standard’ method be devised – controlling chamber/room size and ventilation rate – to facilitate effective comparison between different plant species.

We believe plants should not be considered as a single entity, expected to provide all the above described benefits. There is large performance variability between species, so we recommend consulting literature to ascertain their suitability for a given benefit.

Although some benefits of indoor plants are less clear, when considered as a whole – with all the benefits combined – we believe plants should be considered as a building service, alongside traditional ventilation systems.

Read the full paper at www.cibse.org.uk/symposium 

About the authors
Curtis Gubb and Christian Pfrang, Department of Earth, Geography and Environmental Science, University of Birmingham CXG857@student.bham.ac.uk

Tijana Blanusa and Alistair Griffiths, Science Department, Royal Horticultural Society

Acknowledgements
Curtis Gubb’s PhD project, which forms part of this work, is funded by the Royal Horticultural Society (RHS) and the Engineering and Physics Research Council (EPSRC).

  1. Torpy FR, Irga PJ, Burchett MD. Profiling indoor plants for the amelioration of high CO2 concentrations. Urban Forestry & Urban Greening. 2014;13(2):227-33.
  2. Gubb C, Blanusa T, Griffiths A, Pfrang C. Can houseplants improve indoor air quality by removing CO2 and increasing relative humidity?
  3. Molhave L. Organic compounds as indicators of air pollution. Indoor Air. 2003;13:12-9.
  4. Ekberg LE. VOLATILE ORGANIC-COMPOUNDS IN OFFICE BUILDINGS. Atmospheric Environment. 1994;28(22):3571-5.
  5. Myers I, Maynard RL. Polluted air – outdoors and indoors. Occupational Medicine-Oxford. 2005;55(6):432-8.
  6. WHO guidelines for indoor air quality: selected pollutants. World Health Organisation; 2010.
  7. Afshari A, Matson U, Ekberg LE. Characterization of indoor sources of fine and ultrafine particles: a study conducted in a full-scale chamber. Indoor Air. 2005;15(2):141-50.
  8. Satish U, Mendell MJ, Shekhar K, Hotchi T, Sullivan D, Streufert S, et al. Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance. Environmental Health Perspectives. 2012;120(12):1671-7.
  9. Molhave L, Clausen G, Berglund B, de Ceaurriz J, Kettrup A, Lindvall T, et al. Total volatile organic compounds (TVOC) in indoor air quality investigations. Indoor Air-International Journal of Indoor Air Quality and Climate. 1997;7(4):225-40.
  10. Al-Hemoud A, Al-Awadi L, Al-Khayat A, Behbehani W. Streamlining IAQ guidelines and investigating the effect of door opening/closing on concentrations of VOCs, formaldehyde, and NO2 in office buildings. Building and Environment. 2018;137:127-37.
  11. Dose-response assessment for accessing health risks associated with exposure to hazardous air pollutants: Table 1 prioritized chronic dose response values: United States Environmental Protection Agency; 2014 [Available from: https://www.epa.gov/fera/dose-response- assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.
  12. How to Deal with Sick Building Syndrome (SBS) Guidance for employers ,building owners and building managers. 3 ed. Suffolk, UK: Health and Safety Executive Books; 2000. 37 p.
  13. Weschler CJ, Shields HC. Indoor ozone/terpene reactions as a source of indoor particles. Atmospheric Environment. 1999;33(15):2301-12.
  14. Wolkoff P, Wilkins CK, Clausen PA, Nielsen GD. Organic compounds in office environments – sensory irritation, odor, measurements and the role of reactive chemistry. Indoor Air. 2006;16(1):7- 19.
  15. Wolkoff P, Nielsen GD. Effects by inhalation of abundant fragrances in indoor air – An overview. Environment international.
  16. Yang DS, Pennisi SV, Son K-C, Kays SJ. Screening Indoor Plants for Volatile Organic Pollutant Removal Efficiency. Hortscience. 2009;44(5):1377-81.
  17. Gawronska H, Bakera B. Phytoremediation of particulate matter from indoor air by Chlorophytum comosum L. plants. Air Quality Atmosphere and Health. 2015;8(3):265-72.
  18. Pettit T, Irga PJ, Abdo P, Torpy FR. Do the plants in functional green walls contribute to their ability to filter :particulate matter? Building and Environment. 2017;125:299-307.
  19. Stapleton E, Ruiz-Rudolph P. The potential for indoor ultrafine particle reduction using vegetation under laboratory conditions. Indoor and Built Environment. 2018;27(1):70-83.
  20. Papinchaki HL, Holcom EJ, Best TO, Decoteau DR. Effectiveness of Houseplants in Reducing the Indoor Air Pollutant Ozone. Horttechnology. 2009;19(2):286-90.
  21. Abbass OA, Sailor DJ, Gall ET. Effectiveness of indoor plants for passive removal of indoor ozone. Building and Environment. 2017;119:62-70.
  22. Fjeld T, Veiersted B, Sandvik L, Riise G, Levy F. The effect of indoor foliage plants on health and discomfort symptoms among office workers. Indoor and Built Environment. 1998;7(4):204-9.
  23. Fjeld T. The effect of interior planting on health and discomfort among workers and school children. HortTechnology. 2000;10(1):46-52.
  24. Lim Y-W, Kim H-H, Yang J-Y, Kim K-J, Lee J-Y, Shin D-C. Improvement of Indoor Air Quality by Houseplants in New-built Apartment Buildings. Journal of the Japanese Society for Horticultural Science. 2009;78(4):456-62.
  25. Seppanen OA, Fisk WJ, Mendell MJ. Association of ventilation rates and CO2 concentrations with health and other responses in commercial and institutional buildings. Indoor Air-International Journal of Indoor Air Quality and Climate. 1999;9(4):226-52.
  26. Erdmann CA, Apte MG. Mucous membrane and lower respiratory building related symptoms in relation to indoor carbon dioxide concentrations in the 100-building BASE dataset. Indoor Air. 2004;14:127-34.
  27. Shaughnessy RJ, Haverinen-Shaughnessy U, Nevalainen A, Moschandreas D. The effects of classroom air temperature and outdoor air supply rate on the performance of school work by children. Indoor Air. 2006;16(6):465-8.
  28. Gaihre S, Semple S, Miller J, Fielding S, Turner S. Classroom Carbon Dioxide Concentration, School Attendance, and Educational Attainment. Journal of School Health. 2014;84(9):569-74.
  29. Allen JG, MacNaughton P, Satish U, Santanam S, Vallarino J, Spengler JD. Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: A Controlled Exposure Study of Green and Conventional Office Environments. Environmental Health Perspectives. 2016;124(6):805-12.
  30. Zhang X, Wargocki P, Lian Z. Physiological responses during exposure to carbon dioxide and bioeffluents at levels typically occurring indoors. Indoor Air. 2017;27(1):65-77.
  31. Perez-Lombard L, Ortiz J, Pout C. A review on buildings energy consumption information. Energy and Buildings. 2008;40(3):394-8.
  32. Arundel AV, Sterling EM, Biggin JH, Sterling TD. INDIRECT HEALTH-EFFECTS OF RELATIVE- HUMIDITY IN INDOOR ENVIRONMENTS. Environmental Health Perspectives. 1986;65:351-61.
  33. Berglund LG. Comfort and humidity. Ashrae Journal-American Society of Heating Refrigerating and Air-Conditioning Engineers. 1998;40(8):35-41.
  34. Bin S. A field study of mould growth and indoor health conditions in Auckland dwellings. Architectural Science Review. 2002;45(4):275-84.
  35. Zhang H, Yoshino H. Analysis of indoor humidity environment in Chinese residential buildings. Building and Environment. 2010;45(10):2132-40.
  36. Frankel M, Beko G, Timm M, Gustavsen S, Hansen EW, Madsen AM. Seasonal Variations of Indoor Microbial Exposures and Their Relation to Temperature, Relative Humidity, and Air Exchange Rate. Applied and Environmental Microbiology. 2012;78(23):8289-97.
  37. Sunwoo Y, Chou C, Takeshita J, Murakami M, Tochihara Y. Physiological and subjective responses to low relative humidity in young and elderly men. Journal of Physiological Anthropology. 2006;25(3):229-38.
  38. Lowen AC, Mubareka S, Steel J, Palese P. Influenza virus transmission is dependent on relative humidity and temperature. Plos Pathogens. 2007;3(10):1470-6.
  39. Abusharha AA, Pearce EI. The Effect of Low Humidity on the Human Tear Film. Cornea. 2013;32(4):429-34.
  40. Logue JM, McKone TE, Sherman MH, Singer BC. Hazard assessment of chemical air contaminants measured in residences. Indoor Air. 2011;21(2):92-109.
  41. Cometto-Muniz JE, Abraham MH. Compilation and analysis of types and concentrations of airborne chemicals measured in various indoor and outdoor human environments. Chemosphere. 2015;127:70-86.
  42. Baez A, Padilla H, Garcia R, Torres MD, Rosas I, Belmont R. Carbonyl levels in indoor and outdoor air in Mexico City and Xalapa, Mexico. Science of the Total Environment. 2003;302(1-3):211- 26.
  43. Uchiyama S, Tomizawa T, Tokoro A, Aoki M, Hishiki M, Yamada T, et al. Gaseous chemical compounds in indoor and outdoor air of 602 houses throughout Japan in winter and summer. Environmental Research. 2015;137:364-72.
  44. Zhu J, Wong SL, Cakmak S. Nationally Representative Levels of Selected Volatile Organic Compounds in Canadian Residential Indoor Air: Population-Based Survey. Environmental Science and Technology. 2013;47(23):13276-83.
  45. Son B, Breysse P, Yang W. Volatile organic compounds concentrations in residential indoor and outdoor and its personal exposure in Korea. Environment International. 2003;29(1):79-85.
  46. Adgate JL, Eberly LE, Stroebel C, Pellizzari ED, Sexton K. Personal, indoor, and outdoor VOC exposures in a probability sample of children. Journal of Exposure Analysis and Environmental Epidemiology. 2004;14:S4-S13.
  47. Schlink U, Rehwagen M, Damm M, Richter M, Borte M, Herbarth O. Seasonal cycle of indoor- VOCs: comparison of apartments and cities. Atmospheric Environment. 2004;38(8):1181-90.
  48. Zhu F, Xu J, Ke Y, Huang S, Zeng F, Luan T, et al. Applications of in vivo and in vitro solid-phase microextraction techniques in plant analysis: A review. Analytica Chimica Acta. 2013;794:1-14.
  49. Lawrence AJ, Masih A, Taneja A. Indoor/Outdoor relationships of carbon monoxide and oxides of nitrogen in domestic homes with roadside, urban and rural locations in a central Indian region. Indoor Air. 2005;15(2):76-82.
  50. Spilak MP. Evaluation of building characteristics in 27 dwellings in Denmark and the effect of using particle filtration units on PM concentrations. Building & Environment. 2014;73:55-64.
  51. Burgos S, Ruiz P, Koifman R. Changes to indoor air quality as a result of relocating families from slums to public housing. Atmospheric Environment. 2013;70:179-85.
  52. Seo J, Kato S, Ataka Y, Chino S. Performance test for evaluating the reduction of VOCs in rooms and evaluating the lifetime of sorptive building materials. Building and Environment. 2009;44(1):207-15.
  53. Gunschera J, Mentese S, Salthammer T, Andersen JR. Impact of building materials on indoor formaldehyde levels: Effect of ceiling tiles, mineral fiber insulation and gypsum board. Building and Environment. 2013;64:138-45.
  54. da Silva CF, Stefanowski B, Maskell D, Ormondroyd GA, Ansell MP, Dengel AC, et al. Improvement of indoor air quality by MDF panels containing walnut shells. Building and Environment. 2017;123:427-36.
  55. Guerreiro C, Leeuw Fd, Foltescu V, Ortiz AG, Horálek J. Air Quality In Europe – 2015 Report. European Environment Agency;
  56. Duan H, Liu X, Yan M, Wu Y, Liu Z. Characteristics Of Carbonyls and Volatile Organic Compounds (VOCs) in Residences in Beijing, China. Frontiers of Environmental Science and Engineering. 2016;10(1):73-84.
  57. Fan G, Xie J, Liu J, Yoshino H. Investigation of indoor environmental quality in urban dwellings with schoolchildren in Beijing, China. Indoor and Built Environment. 2016:1-23.
  58. Cheng M, Galbally IE, Molloy SB, Selleck PW, Keywood MD, Lawson SJ, et al. Factors controlling volatile organic compounds in dwellings in Melbourne, Australia. Indoor Air. 2016;26(2):219-30.
  59. Molloy SB, Cheng M, Galbally IE, Keywood MD, Lawson SJ, Powell JC, et al. Indoor air quality in typical temperate zone Australian dwellings. Atmospheric Environment. 2012;54:400-7.
  60. Du Z, Mo J, Zhang Y, Xu Q. Benzene, toluene and xylenes in newly renovated homes and associated health risk in Guangzhou, China. Building and Environment. 2014;72:75-81.
  61. Kumar A, Singh BP, Punia M, Singh D, Kumar K, Jain VK. Determination of volatile organic compounds and associated health risk assessment in residential homes and hostels within an academic institute, New Delhi. Indoor Air. 2014;24(5):474-83.
  62. Hazrati S, Rostami R, Farjaminezhad M, Fazlzadeh M. Preliminary assessment of BTEX concentrations in indoor air of residential buildings and atmospheric ambient air in Ardabil, Iran. Atmospheric Environment. 2016;132:91-7.
  63. Chin JY, Godwin C, Jia C, Robins T, Lewis T, Parker E, et al. Concentrations and risks of p- dichlorobenzene in indoor and outdoor air. Indoor Air. 2013;23(1):40-9.
  64. Abdul-Wahab SA, Salem N, Ali S. Evaluation of indoor air quality in a museum (Bait Al Zubair) and residential homes. Indoor and Built Environment. 2015;24(2):244-55.
  65. Romagnoli P, Balducci C, Perilli M, Vichi F, Imperiali A, Cecinato A. Indoor air quality at life and work environments in Rome, Italy. Environmental Science and Pollution Research. 2016;23(4):3503-16.
  66. Holm S, Balmes J, Gillette D, Hartin K, Seto E, Lindeman D, et al. Cooking behaviors are related to household particulate matter exposure in children with asthma in the urban East Bay Area of Northern California. PLoS One. 2018;13(6):e0197199.
  67. Clements N, Keady P, Emerson JB, Fierer N, Miller SL. Seasonal variability of airborne particulate matter and bacterial concentrations in colorado homes. Atmosphere. 2018;9(4):<xocs:firstpage xmlns:xocs=””/>.
  68. Morawska L, Ayoko GA, Bae GN, Buonanno G, Chao CYH, Clifford S, et al. Airborne particles in indoor environment of homes, schools, offices and aged care facilities: The main routes of exposure. Environment International. 2017;108:75-83.
  69. Barraza F, Jorquera H, Valdivia G, Montoya LD. Indoor PM2.5 in Santiago, Chile, spring 2012: Source apportionment and outdoor contributions. Atmospheric Environment. 2014;94(C):692-700.
  70. Prasauskas T, Martuzevicius D, Krugly E, Ciuzas D, Stasiulaitiene I, Sidaraviciute R, et al. Spatial and temporal variations of particulate matter concentrations in multifamily apartment buildings. Building and Environment. 2014;76(C):10-7.
  71. Takahashi M, Higaki A, Nohno M, Kamada M, Okamura Y, Matsui K, et al. Differential assimilation of nitrogen dioxide by 70 taxa of roadside trees at an urban pollution level. Chemosphere. 2005;61(5):633-9.
  72. Nowak DJ, Crane DE, Stevens JC. Air pollution removal by urban trees and shrubs in the United States. Urban Forestry & Urban Greening. 2006;4(3-4):115-23.
  73. Orwell RL, Wood RL, Tarran J, Torpy F, Burchett MD. Removal of benzene by the indoor plant/substrate microcosm and implications for air quality. Water Air and Soil Pollution. 2004;157(1- 4):193-207.
  74. Irga PJ, Torpy FR, Burchett MD. Can hydroculture be used to enhance the performance of indoor plants for the removal of air pollutants? Atmospheric Environment. 2013;77:267-71.
  75. Kim KJ, Kil MJ, Song JS, Yoo EH, Son K-C, Kays SJ. Efficiency of volatile formaldehyde removal by indoor plants: Contribution of aerial plant parts versus the root zone. Journal of the American Society for Horticultural Science. 2008;133(4):521-6.
  76. Xu Z, Wang L, Hou H. Formaldehyde removal by potted plant-soil systems. Journal of Hazardous Materials. 2011;192(1):314-8.
  77. Torpy FR, Zavattaro M, Irga PJ. Green wall technology for the phytoremediation of indoor air: a system for the reduction of high CO2 concentrations. Air Quality Atmosphere and Health. 2017;10(5):575-85.
  78. Shendell DG, Prill R, Fisk WJ, Apte MG, Blake D, Faulkner D. Associations between classroom CO2 concentrations and student attendance in Washington and Idaho. Indoor Air. 2004;14(5):333-41.
  79. Tsai D-H, Lin J-S, Chan C-C. Office Workers’ Sick Building Syndrome and Indoor Carbon Dioxide Concentrations. Journal of Occupational and Environmental Hygiene. 2012;9(5):345-51.
  80. Charoenkit S, Yiemwattana S. Living walls and their contribution to improved thermal comfort and carbon emission reduction: A review. Building and Environment. 2016;105:82-94.
  81. Raza SH, Shylaja G, Murthy MSR, Bhagyalakshmi O. THE CONTRIBUTION OF PLANTS FOR CO2 REMOVAL FROM INDOOR AIR. Environment International. 1991;17(4):343-7.
  82. Oh GS, Jung GJ, Seo MH, Im YB. Experimental study on variations of CO2 concentration in the presence of indoor plants and respiration of experimental animals. Horticulture Environment and Biotechnology. 2011;52(3):321-9.
  83. Pennisi SV, van Iersel MW. Quantification of Carbon Assimilation of Plants in Simulated and In Situ Interiorscapes. Hortscience. 2012;47(4):468-76.
  84. Pegas PN, Alves CA, Nunes T, Bate-Epey EF, Evtyugina M, Pio CA. Could Houseplants Improve Indoor air Quality in Schools? Journal of Toxicology and Environmental Health-Part a-Current Issues. 2012;75(22-23):1371-80.
  85. Lohr VI, PearsonMims CH. Particulate matter accumulation on horizontal surfaces in interiors: Influence of foliage plants. Atmospheric Environment. 1996;30(14):2565-8.
  86. Jeong SJ, Song JS, Kim WS, Lee DW, Kim HD, Kim KJ, et al. Evaluation of Selected Foliage Plants for Improvement of Indoor Humidity. Horticulture Environment and Biotechnology. 2008;49(6):439-46.
  87. De Kempeneer L, Sercu B, Vanbrabant W, Van Langenhove H, Verstraete W. Bioaugmentation of the phyllosphere for the removal of toluene from indoor air. Applied Microbiology and Biotechnology. 2004;64(2):284-8.
  88. Tani A, Kato S, Kajii Y, Wilkinson M, Owen S, Hewitt N. A proton transfer reaction mass spectrometry based system for determining plant uptake of volatile organic compounds. Atmospheric Environment. 2007;41(8):1736-46.
  89. Siswanto D, Chhon Y, Thiravetyan P. Uptake and degradation of trimethylamine by Euphorbia milii. Environmental Science and Pollution Research. 2016;23(17):17067-76.
  90. Irga PJ, Pettit TJ, Torpy FR. The phytoremediation of indoor air pollution: a review on the technology development from the potted plant through to functional green wall biofilters. Reviews in Environmental Science and Bio-Technology. 2018;17(2):395-415.
  91. Kim KJ, Khalekuzzaman M, Suh JN, Kim HJ, Shagol C, Kim H-H, et al. Phytoremediation of volatile organic compounds by indoor plants: a review. Horticulture Environment and Biotechnology. 2018;59(2):143-57.
biophilia Health and wellbeing indoor air quality