Volatile organic compounds or VOCs are molecules containing carbon which are predominantly in the gaseous state at room temperature. For example, most of the odorous molecules in flowers and scented products are VOCs [1]. Because of their gaseous state and their small size, VOCs can interact with our respiratory system. Therefore, VOCs raise concerns regarding their influence on asthma and allergic disorders such as eczema or respiratory irritations. For instance, exposure to VOCs during pregnancy can lead to the development of eczema amongst newborns [2]. As we spend about 90 % of our time indoors [3], it is particularly important to ensure that the chemical quality of indoor air is not causing any respiratory symptoms.
This article will present the possible sources of indoor VOCs, how VOCs impact on people with asthma and allergy and discuss the ability of air cleaners to reduce VOCs in the indoor environment.
Sources of indoor air VOCs
Amongst VOCs indoor air, several groups of compounds coexist. The most common ones are the following
| Type of VOCs | Molecules belonging to this type | Sources |
| BTEX | Benzene, toluene, ethylbenzene & xylene | Electronic devices, indoor smoking, cooking equipment(4), building materials(5) |
| Carbonyl Compounds | Formaldehyde, acetaldehyde, etc. | Building materials(5), textiles, furniture, combustion processes(6) |
| Terpenes | Limonene, alpha-pinene, Linalool, geraniol, dihydromyrcenol, etc. | Electronic devices,(7), essential oils, (8), air fresheners(9), fragranced products(1,9) |
| Alkanes | Nonane, hexane, methylcyclohexane, etc. | Electronic devices(7), adhesives(10), food cooking, consumer products(11) |
| PGE | Propylene, toluene, ethylbenzene & xylenes | Cleaning products, Paints(12) |
In other words, VOCs come from different sources:
- Building materials, which are the biggest source of indoor VOCs
- Electronic equipment
- Cleaning products containing PGEs
- Furniture
Building Materials
Building materials such as paints, solvents or varnishes have a key role in indoor air quality. Indeed, they release 40% of indoor air VOCs [5,12] amongst which are formaldehyde, acetaldehyde, toluene, acetone, propylene glycol and xylenes. As VOCs evaporate quite quickly, newly built homes tend to release more VOCs than older ones, especially during the first year after construction [13]. Furniture releases roughly the same VOCs as building materials [14].
Electronic Equipment
Electronic equipment releases VOCs too: alkanes, formaldehyde, acetaldehyde, terpenes and BTEX aromatic compounds are the most commonly found VOCs in electronics. VOCs in electronic equipment come from their plastic shell but also from the products they use, such as ink for printers. When used, most electronic devices heat up, promoting the evaporation of VOCs. This is particularly true for photocopiers, which emit more VOCs than most of electronic equipment [7].
Cooking
Cooking and combustion processes are also associated with the release of VOCs. Some cooking processes have a greater impact than others. For instance, fryers and barbecues are amongst the biggest sources of VOCs in cooking. Barbecues release acetaldehyde and hexanal when used, up to 8 times the limiting values set by the US Environmental Protection Agency (EPA) [15].
Consumer Products
Consumer products such as cleaning products, air fresheners, essential oils and self-care products do emit VOCs, especially when they are scented products [1]. More specifically, they emit terpenes, a group of odorous molecules often found in flowers or fruits [9]. Because of their chemical structure, terpenes are able to react with ozone to produce secondary organic aerosols, which can lead to elevated exposure to fine particles [16]. Cleaning products also emit PGEs [12].
Impact of VOCs on asthma and allergic disorders
VOC exposure has been associated with eye and respiratory irritations, eczema as well as asthma [2]. However, different effects of VOCs on human health have been reported regarding the type of molecules involved.
PGEs
Exposition to PGEs such as propylene glycol has been correlated to the development of allergic symptoms, eczema, rhinitis, asthma and IgE sensitization in children under 8 years old [17].
Alkanes
Investigations on alkanes found no associations with dermatitis or allergic respiratory symptoms [18]. One study linked N-undecane to asthma [19]. Nevertheless, it is still important to respect the exposure limit values to such molecules and to ventilate kitchens where they can accumulate [15].
Terpenes
Terpenes undergo oxidation processes upon air exposure [20]. Yet, if terpenes are not known to be allergenic, oxidized terpenes are associated with skin irritation and contact allergy [20,21]. Allergies to oxidized linalool and limonene are frequent and affect around 1% of the population [21,22,23].
Formaldehyde
Exposure to formaldehyde, a carbonyl compound, is known to induce skin allergic reactions and respiratory irritations [2,24]. Children whose mothers were exposed to formaldehyde during pregnancy are more prone to develop atopic eczema [2]. It has also been linked to childhood asthma [25]. Acetaldehyde does not have such effects but it causes bronchoconstriction amongst asthmatic persons [26] and it has been associated with an exacerbation of allergic airway inflammations [27].
BTEX
BTEX exposure has been associated with asthma and rhinitis in adults [19]. Children are also at risk as the presence of benzene in air has been linked to asthma and pulmonary infections [28,29]. Benzene, chlorobenzene and ethylbenzene trigger the production of antibodies when inhaled, leading to allergy sensitization [30].
In short, VOCs exposure is correlated to allergic reactions and asthma. Some VOCs such as formaldehyde or PGEs induce these reactions whereas others like acetaldehyde enhance respiratory symptoms in allergic or asthmatic persons. Therefore, it is critical to maintain an indoor air with low levels of VOCs for everyone.
Air treatment devices and their impact on indoor air VOCs
Different types of air purifiers exist and are commercially available nowadays. Some of them have an impact on VOCs while others don’t. Indeed, air fibrous filters (HEPA, ULPA, etc.) are designed to hold back dust particles and microorganisms but are not able to filter out VOCs [31]. Used fibrous filters can even emit secondary VOCs if they are not replaced as they should be [32]. Ionizers and electrostatic air purifiers, which use charges to precipitate or capture small particles are also inefficient against VOC pollution [33, 34,35].
Ozone generators
Ozone generators can oxidize some VOCs such as terpenes. They are not an appropriate method to purify air as oxidized terpenes cause skin irritations [21]. They cannot affect other VOCs [35] because they need to keep ozone concentrations under 0.00001% to avoid acute toxicity [36]. Generally speaking, ozone generators should be avoided as their safety is not ensured.
Thermal plasma air purifiers
Non-thermal plasma air purifying systems can degrade up to 11% of certain VOCs like cyclohexene [37]. To do so, they release ozone which, as previously mentioned, raises health concerns [38]. Thermal plasmas are less prone to release ozone [38] and can be used to remove VOCs in industrial environments. They are not suited to treat indoor air as the VOCs concentrations in domestic indoor air are lower [39].
There are two air treatment technologies widely available which are designed to remove VOCs from indoor air.
- Materials which will capture the VOCs on their surface.
This phenomenon is called sorption and involves mostly weak physical bonds between the molecule and the sorptive material (adsorption). Sorption filtration using materials like activated carbon is an efficient option for the removal of VOCs [35,40] and it does not cause any secondary pollution when used. As adsorption does not degrade VOCs, sorption filters must be changed regularly. If possible, they should be sent back to the manufacturer as they can be regenerated [41].
- Photocatalytic oxidation (PCO)
The second option is to use photocatalytic oxidation (PCO), activated with UV light or fluorescent light, which degrade most of the VOCs in carbon dioxide CO2 and water [35,42]. PCO systems often use titanium dioxide as their catalyst [43]. Depending on its design, the efficiency of PCO systems may differ [35]. Furthermore, the chemical processes involved in PCO systems need several steps to go from VOCs to CO2. Partial oxidation can lead to the emission of secondary VOCs [44]. Therefore, it is crucial to select systems which maximize the contact time between the air and the photocatalyst to obtain total oxidation of VOCs. To do so, these systems may use a pleated support for the photocatalyst [45] and low flow rates [42].
In Summary
To conclude, there are a wide variety of VOCs coming from different sources. Building materials are the biggest source of indoor VOCs but they are not the only one [5]. Electronic devices, especially photocopiers, and cleaning products containing PGEs (polyethylene glycol or glycol ethers) should not be used in rooms where children live [7, 12]. Indeed, the VOCs released by these sources lead to the development of respiratory and skin allergies as well as asthma [2]. Some of them even enhance allergic reactions [27].
For everyone’s safety, air treatment systems can be used to lower the VOCs concentration. To act against VOCs, the air treatment devices need to have a sorptive filter such as activated carbon [35,40] or a photocatalytic oxidation system, often using titanium dioxide TiO2 [42].
About the author
Thanks to Dr Aliénor Dutheil de la Rochère for this insightful article.
Keywords
allergies, asthma, VOCs, volatile organic compounds, indoor air, indoor environment, indoor air quality, allergen, filter, air filter, HEPA filter, particles, dust, particulates, air purifier, air cleaner, chemicals, formaldehyde, acetaldehyde, terpenes, alkanes, respiratory symptoms
References
[1] Potera, Carol. 2011. “INDOOR AIR QUALITY: Scented Products Emit a Bouquet of VOCs.” Environmental Health Perspectives 119 (1): A16.
[2] Jie, Yu, Noor Hassim Ismail, Xu jie, and Zaleha Md Isa. 2011. “Do Indoor Environments Influence Asthma and Asthma-Related Symptoms among Adults in Homes? A Review of the Literature.” Journal of the Formosan Medical Association 110 (9): 555–63. https://doi.org/10.1016/j.jfma.2011.07.003.
[3] Klepeis, Neil E., William C. Nelson, Wayne R. Ott, John P. Robinson, Andy M. Tsang, Paul Switzer, Joseph V. Behar, Stephen C. Hern, and William H. Engelmann. 2001. “The National Human Activity Pattern Survey (NHAPS): A Resource for Assessing Exposure to Environmental Pollutants.” Journal of Exposure Science & Environmental Epidemiology 11 (3): 231–52. https://doi.org/10.1038/sj.jea.7500165.
[4] Guo, H, S. C Lee, W. M Li, and J. J Cao. 2003. “Source Characterization of BTEX in Indoor Microenvironments in Hong Kong.” Atmospheric Environment 37 (1): 73–82. https://doi.org/10.1016/S1352-2310(02)00724-0.
[5] Missia, Dafni A., E. Demetriou, N. Michael, E. I. Tolis, and J. G. Bartzis. 2010. “Indoor Exposure from Building Materials: A Field Study.” Atmospheric Environment 44 (35): 4388–95. https://doi.org/10.1016/j.atmosenv.2010.07.049.
[6] Salthammer, Tunga. 2019. “Formaldehyde Sources, Formaldehyde Concentrations and Air Exchange Rates in European Housings.” Building and Environment 150 (March): 219–32. https://doi.org/10.1016/j.buildenv.2018.12.042.
[7] Carmen, Cacho, Ventura Silva Gabriela, Martins Anabela, Oliveira Fernandes Eduardo, Dikaia E. Saraga, Dimitroulopoulou Chrysanthi, G. Bartzis John, Rembges Diana, Barrero Josefa, and Kotzias Dimitrios. 2013. “Air Pollutants in Office Environments and Emissions from Electronic Equipment: A Review.” Fresenius Environmental Bulletin 22 (9): 2488–97.
[8] Angulo, Shadia. 2019. “Emissions of Terpenes from the Use of Essential-Oil-Based Household Products under Realisatic Condition : Ompact on Indoor Air Quality.” http://www.theses.fr/s239915.
[9] Bartzis, J., P. Wolkoff, M. Stranger, G. Efthimiou, E. I. Tolis, F. Maes, A. W. Nørgaard, et al. 2015. “On Organic Emissions Testing from Indoor Consumer Products’ Use.” Journal of Hazardous Materials 285 (March): 37–45. https://doi.org/10.1016/j.jhazmat.2014.11.024.
[10] Girman, J. R., A. T. Hodgson, A. S. Newton, and A. W. Winkes. 1986. “Emissions of Volatile Organic Compounds from Adhesives with Indoor Applications.” Environment International, Indoor Air Quality, 12 (1): 317–21. https://doi.org/10.1016/0160-4120(86)90045-0.
[11] Hasheminassab, Sina, Nancy Daher, Martin M. Shafer, James J. Schauer, Ralph J. Delfino, and Constantinos Sioutas. 2014. “Chemical Characterization and Source Apportionment of Indoor and Outdoor Fine Particulate Matter (PM2.5) in Retirement Communities of the Los Angeles Basin.” Science of The Total Environment 490 (August): 528–37. https://doi.org/10.1016/j.scitotenv.2014.05.044.
[12] Choi, Hyunok, Norbert Schmidbauer, John Spengler, and Carl-Gustaf Bornehag. 2010. “Sources of Propylene Glycol and Glycol Ethers in Air at Home.” International Journal of Environmental Research and Public Health 7 (12): 4213–37. https://doi.org/10.3390/ijerph7124213.
[13] Park, J. S., and K. Ikeda. 2006. “Variations of Formaldehyde and VOC Levels during 3 Years in New and Older Homes.” Indoor Air 16 (2): 129–35. https://doi.org/10.1111/j.1600-0668.2005.00408.x.
[14] Qi, Yiqing, Liming Shen, Jilei Zhang, Jia Yao, Rong Lu, and Tetsuo Miyakoshi. 2019. “Species and Release Characteristics of VOCs in Furniture Coating Process.” Environmental Pollution 245 (February): 810–19. https://doi.org/10.1016/j.envpol.2018.11.057.
[15] Wang, Hongli, Zhiyuan Xiang, Lina Wang, Shengao Jing, Shengrong Lou, Shikang Tao, Jing Liu, et al. 2018. “Emissions of Volatile Organic Compounds (VOCs) from Cooking and Their Speciation: A Case Study for Shanghai with Implications for China.” Science of The Total Environment 621 (April): 1300–1309. https://doi.org/10.1016/j.scitotenv.2017.10.098.
[16] Sarwar, Golam, David A. Olson, Richard L. Corsi, and Charles J. Weschler. 2004. “Indoor Fine Particles: The Role of Terpene Emissions from Consumer Products.” Journal of the Air & Waste Management Association 54 (3): 367–77. https://doi.org/10.1080/10473289.2004.10470910.
[17] Choi, Hyunok, Norbert Schmidbauer, Jan Sundell, Mikael Hasselgren, John Spengler, and Carl-Gustaf Bornehag. 2010. “Common Household Chemicals and the Allergy Risks in Pre-School Age Children.” PLOS ONE 5 (10): e13423. https://doi.org/10.1371/journal.pone.0013423.
[18] Nurmatov, Ulugbek B., Nara Tagieva, Sean Semple, Graham Devereux, and Aziz Sheikh. 2013. “Volatile Organic Compounds and Risk of Asthma and Allergy: A Systematic Review and Meta-Analysis of Observational and Interventional Studies.” Primary Care Respiratory Journal 22 (1): S9–15. https://doi.org/10.4104/pcrj.2013.00010.
[19] Billionnet, Cécile, Emilie Gay, Séverine Kirchner, Bénédicte Leynaert, and Isabella Annesi-Maesano. 2011. “Quantitative Assessments of Indoor Air Pollution and Respiratory Health in a Population-Based Sample of French Dwellings.” Environmental Research 111 (3): 425–34. https://doi.org/10.1016/j.envres.2011.02.008.
[20] Bäcktorp, Carina, Lina Hagvall, Anna Börje, Ann-Therese Karlberg, Per-Ola Norrby, and Gunnar Nyman. 2008. “Mechanism of Air Oxidation of the Fragrance Terpene Geraniol.” Journal of Chemical Theory and Computation 4 (1): 101–6. https://doi.org/10.1021/ct7001495.
[21] Christensson, Johanna Bråred, Pia Forsström, Ann-Marie Wennberg, Ann-Therese Karlberg, and Mihály Matura. 2009. “Air Oxidation Increases Skin Irritation from Fragrance Terpenes.” Contact Dermatitis 60 (1): 32–40. https://doi.org/10.1111/j.1600-0536.2008.01471.x.
[22] Audrain, H., C. Kenward, C. R. Lovell, C. Green, A. D. Ormerod, J. Sansom, M. M. U. Chowdhury, et al. 2014. “Allergy to Oxidized Limonene and Linalool Is Frequent in the U.K.” British Journal of Dermatology 171 (2): 292–97. https://doi.org/10.1111/bjd.13037.
[23] Matura, Mihaly, Maria Sköld, Anna Börje, Klaus E. Andersen, Magnus Bruze, Peter Frosch, An Goossens, et al. 2005. “Selected Oxidized Fragrance Terpenes Are Common Contact Allergens.” Contact Dermatitis 52 (6): 320–28. https://doi.org/10.1111/j.0105-1873.2005.00605.x.
[24] Yeatts, Karin B., Mohamed El-Sadig, David Leith, William Kalsbeek, Fatma Al-Maskari, David Couper, William E. Funk, et al. 2012. “Indoor Air Pollutants and Health in the United Arab Emirates.” Environmental Health Perspectives 120 (5): 687–94. https://doi.org/10.1289/ehp.1104090.
[25] McGwin, Gerald, Jeffrey Lienert, and John I. Kennedy. 2010. “Formaldehyde Exposure and Asthma in Children: A Systematic Review.” Environmental Health Perspectives 118 (3): 313–17. https://doi.org/10.1289/ehp.0901143.
[26] Prieto, L., F. Sánchez-Toril, B. Brotons, S. Soriano, R. Casañ, and J. L. Belenguer. 2000. “Airway Responsiveness to Acetaldehyde in Patients with Asthma: Relationship to Methacholine Responsiveness and Peak Expiratory Flow Variation.” Clinical and Experimental Allergy: Journal of the British Society for Allergy and Clinical Immunology 30 (1): 71–78. https://doi.org/10.1046/j.1365-2222.2000.00672.x.
[27] Kawano, T., Tetsuya Kawano, Hiroto Matsuse, Susumu Fukahori, Tomoko Tsuchida, Tomoya Nishino, Chizu Fukushima, and Shigeru Kohno. 2012. “Acetaldehyde at a Low Concentration Synergistically Exacerbates Allergic Airway Inflammation as an Endocrine-Disrupting Chemical and as a Volatile Organic Compound.” Respiration 84 (2): 135–41. https://doi.org/10.1159/000337112.
[28] Ferrero, Amparo, Carmen Íñiguez, Ana Esplugues, Marisa Estarlich, and Ferran Ballester. 2014. “Benzene Exposure and Respiratory Health in Children: A Systematic Review of Epidemiologic Evidences.” Journal of Pollution Effects & Control 2 (2): 1–13. https://doi.org/10.4172/2375-4397.1000114.
[29] Rive, S., M. Hulin, N. Baiz, Y. Hassani, H. Kigninlman, Y. Toloba, D. Caillaud, and I. Annesi-Maesano. 2013. “Urinary S-PMA Related to Indoor Benzene and Asthma in Children.” Inhalation Toxicology 25 (7): 373–82. https://doi.org/10.3109/08958378.2013.790522.
[30] Lehmann, I., M. Rehwagen, U. Diez, A. Seiffart, U. Rolle-Kampczyk, M. Richter, H. Wetzig, M. Borte, O. Herbarth, and Leipzig Allergy Risk Children Study. 2001. “Enhanced in Vivo IgE Production and T Cell Polarization toward the Type 2 Phenotype in Association with Indoor Exposure to VOC: Results of the LARS Study.” International Journal of Hygiene and Environmental Health 204 (4): 211–21. https://doi.org/10.1078/1438-4639-00100.
[31] Mao, N. 2016. “10 – Nonwoven Fabric Filters.” In Advances in Technical Nonwovens, edited by George Kellie, 273–310. Woodhead Publishing Series in Textiles. Woodhead Publishing. https://doi.org/10.1016/B978-0-08-100575-0.00010-3.
[32] Pei, Jingjing, and Lili Ji. 2018. “Secondary VOCs Emission from Used Fibrous Filters in Portable Air Cleaners and Ventilation Systems.” Building and Environment 142 (September): 464–71. https://doi.org/10.1016/j.buildenv.2018.06.039.
[33] Lee, Byung Uk, Mikhail Yermakov, and Sergey A. Grinshpun. 2004. “Removal of Fine and Ultrafine Particles from Indoor Air Environments by the Unipolar Ion Emission.” Atmospheric Environment 38 (29): 4815–23. https://doi.org/10.1016/j.atmosenv.2004.06.010.
[34] Chen, Longwen, Evelyne Gonze, Michel Ondarts, Jonathan Outin, and Yves Gonthier. 2020. “Electrostatic Precipitator for Fine and Ultrafine Particle Removal from Indoor Air Environments.” Separation and Purification Technology, April, 116964. https://doi.org/10.1016/j.seppur.2020.116964.
[35] Chen, Wenhao, Jianshun S. Zhang, and Zhibin Zhang. 2005. “Performance of Air Cleaners for Removing Multiple Volatile Organic Compounds in Indoor Air.” In ASHRAE Transactions, 111 PART 1:1101–14. Amer. Soc. Heating, Ref. Air-Conditoning Eng. Inc. https://experts.syr.edu/en/publications/performance-of-air-cleaners-for-removing-multiple-volatile-organi.
[36] Lippmann, Morton. 1989. “HEALTH EFFECTS OF OZONE A Critical Review.” JAPCA 39 (5): 672–95. https://doi.org/10.1080/08940630.1989.10466554.
[37] Schmid, Stefan, Matthias C. Jecklin, and Renato Zenobi. 2010. “Degradation of Volatile Organic Compounds in a Non-Thermal Plasma Air Purifier.” Chemosphere 79 (2): 124–30. https://doi.org/10.1016/j.chemosphere.2010.01.049.
[38] Laroussi, M. 2002. “Nonthermal Decontamination of Biological Media by Atmospheric-Pressure Plasmas: Review, Analysis, and Prospects.” IEEE Transactions on Plasma Science 30 (4): 1409–15. https://doi.org/10.1109/TPS.2002.804220.
[39] Heberlein, Joachim, and Anthony B. Murphy. 2008. “Thermal Plasma Waste Treatment.” Journal of Physics D: Applied Physics 41 (5): 053001. https://doi.org/10.1088/0022-3727/41/5/053001.
[40] Navarri, P, D Marchal, and A Ginestet. 2001. “Activated Carbon Fibre Materials for VOC Removal.” Filtration & Separation 38 (1): 33–40. https://doi.org/10.1016/S0015-1882(01)80150-6.
[41] Kim, Ki-Joong, Chan-Soon Kang, Young-Jae You, Min-Chul Chung, Myung-Wu Woo, Woon-Jo Jeong, Nam-Cook Park, and Ho-Geun Ahn. 2006. “Adsorption–Desorption Characteristics of VOCs over Impregnated Activated Carbons.” Catalysis Today, Advances in Catalysis and Catalytic Materials for Energy and Environmental Protection, 111 (3): 223–28. https://doi.org/10.1016/j.cattod.2005.10.030.
[42] Chapuis, Yannick, Danilo Klvana, Christophe Guy, and Jitka Kirchnerova. 2002. “Photocatalytic Oxidation of Volatile Organic Compounds Using Fluorescent Visible Light.” Journal of the Air & Waste Management Association (1995) 52 (7): 845–54. https://doi.org/10.1080/10473289.2002.10470816.
[43] Mo, Jinhan, Yinping Zhang, Qiujian Xu, Jennifer Joaquin Lamson, and Rongyi Zhao. 2009. “Photocatalytic Purification of Volatile Organic Compounds in Indoor Air: A Literature Review.” Atmospheric Environment 43 (14): 2229–46. https://doi.org/10.1016/j.atmosenv.2009.01.034.
[44] Sun, Yuexia, Lei Fang, David P. Wyon, Armin Wisthaler, Love Lagercrantz, and Peter Strøm-Tejsen. 2008. “Experimental Research on Photocatalytic Oxidation Air Purification Technology Applied to Aircraft Cabins.” Building and Environment, Indoor Air 2005: Modeling, Assessment, and Control of Indoor Air Quality, 43 (3): 258–68. https://doi.org/10.1016/j.buildenv.2006.06.036.
[45] Hequet, Valérie, Louis Olivier, Vanessa Maroga Mboula, Cécile Raillard, Albert Subrenat, and Laurence Le Coq. 2016. “Influence of Operating Parameters on Photocatalytic Oxidation Treatment Efficiency: Contact Time Investigation.” In The 14th International Conference on Indoor Air Quality and Climate (Indoorair 2016). Gand, Belgium. https://hal.archives-ouvertes.fr/hal-02368485.