This article describes a highly specialized aspect of its subject in the "Terminology and legal definitions" section. Please help Wikipedia by adding more general information.
Volatile organic compounds (VOCs) are gases or vapours emitted by various solids or liquids, many of which have short- and long-term adverse health effects. Household products that emit VOCs include paint, paint strippers, cleaning supplies, pesticides, glues and adhesives, building materials and furnishings. Consequently, concentrations of many VOCs are higher indoors (up to ten times higher) than outdoors[5]. Fuels such as gasoline (petrol) and diesel also release VOCs.
VOCs are organic chemical compounds that have high enough vapor pressures under normal conditions to significantly vaporize and enter the atmosphere. A wide range of carbon-based molecules, such as aldehydes, ketones, and other light hydrocarbons are VOCs. The term often is used in a legal or regulatory context and in such cases the precise definition is a matter of law. These definitions can be contradictory and may contain "loopholes"; e.g. exceptions, exemptions, and exclusions. The United States Environmental Protection Agency (EPA) defines a VOC as any organic compound that participates in a photoreaction; others believe this definition is very broad and vague as organics that are not volatile in the sense that they vaporize under normal conditions can be considered volatile by this EPA definition. The term may refer both to well characterized organic compounds and to mixtures of variable composition.
[edit] Definitions
There is no clear and widely supported definition of a VOC. VOC is a term used more in relation to air quality and environmental studies. From a chemistry viewpoint “Volatile Organic Compound” can mean any organic compound (all chemical compounds containing carbon with exceptions) that is volatile (evaporating or vaporizing readily under normal conditions). This is a very broad set of chemicals. Definitions vary depending on the particular context. There are many other widely used terms that are a subclass of VOCs (see below).
[edit] Canada
Health Canada classes VOCs as organic compounds that have boiling points roughly in the range of 50 to 250 °C (120 to 480 °F). The emphasis is placed on commonly encountered VOCs which would have an effect on air quality. [1]
[edit] European Union
A VOC is any organic compound having an initial boiling point less than or equal to 250 °C measured at a standard atmospheric pressure of 101.3 kPa and can do damage to visual or audible senses. [2]
[edit] United States
A VOC has high vapor pressure and low water solubility. [3] The US EPA’s Terms of Environment defines a VOC as any organic compound that participates in atmospheric photochemical reactions except those designated by the EPA as having negligible photochemical reactivity. [4] Under the Code of Federal Regulations it is similarly defined as any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical reactions. [5]
[edit] UK coatings classification
The British coatings industry has adopted a VOC labelling scheme for all decorative coatings to inform customers about the levels of organic solvents and other volatile materials present. Coatings manufacturers use standard terminology, text and categories for all products.[6] Information is provided according to five ‘bands,’ and manufacturers may label products with either a British Coatings Federation text box on the back panel, or a graphical globe symbol, the latter subject to licensing from B&Q plc. Both styles of labels contain the same text, and warn that VOCs contribute to atmospheric pollution.
The five bands are:
| Name |
Range |
| Minimal |
0% ≤ VOC content ≤ 0.29% |
| Low |
0.3% ≤ VOC content ≤ 7.99% |
| Medium |
8% ≤ VOC content ≤ 24.99% |
| High |
25% ≤ VOC content ≤ 50% |
| Very High |
50% < VOC content |
An example of text box labelling for the Minimal band is shown below, while examples of the graphical globe symbols may be seen on websites of some British coatings companies.[7]
[edit] Terminology and legal definitions
There are a number of different ways to collectively refer to those chemical compounds that participate in photochemical reactions.
That is, those that react with other pollutants, in the presence of sunlight, to form tropospheric ozone.
Some of the more common terms are:
| Abbreviation |
Term |
| NMHC |
Non-methane hydrocarbons |
| NMOG |
Non-methane organic gases |
| NMVOC |
Non-methane volatile organic compounds |
| ROG |
Reactive organic gases |
| SVOC |
Semi-volatile organic compounds |
| TOG |
Total organic gases |
| TVOC |
Total volatile organic compounds |
| VOC |
Volatile organic compounds |
While all these terms are used, it is not always clear which pollutants are included in each term. The term "VOC" has the advantage of having precise definitions codified by regulators such as the European Parliament and the US EPA.
Worldwide, legal definitions of the term "VOC" are in many respects, more a matter of policy than a matter of science. For example, because the US EPA Code of Federal Regulations (CFR) has characterized a compound as having "negligible photochemical reactivity" it does not necessarily imply that it is, at any particular time, less reactive than those compounds which are not on the list. Since first establishing the list of exempt compounds in 1977, the EPA has added several to the list, and frequently has several petitions undergoing review.
The traditional US standard to determine if a compound is a non-VOC is to compare its reactivity to that of ethane, which was the least reactive compound on the original list. Unfortunately, this is a very difficult comparison to make as it is frequently impossible to duplicate the real-world conditions in a laboratory. To complicate the issue, typical real-world conditions are different from day to day and from place to place. However, there is ongoing study on the use of a compound's reactivity as a better tool for pollution control regulation than the "is or isn't" approach currently in use.[8]
[edit] Chemical properties
[edit] Applications
[edit] Sources of VOCs
VOCs can be found indoors and outdoors.
The most common VOC is methane, a greenhouse gas sometimes excluded from analysis of other VOCs using the term non-methane VOCs, or NMVOCs.[9] Other terms used in pollution regulations include NMOG - "non-methane organic gas", and NMHC - "non-methane hydrocarbons".[10]
Major worldwide sources of atmospheric methane include wetlands, ruminants such as cows, energy use, rice agriculture, landfills, and burning biomass such as wood.[11] Methane is the primary component of natural gas.[12]
It appears that untreated exhaust emissions of vehicles, such as buses, trucks and cars, that run on compressed natural gas have the highest VOC emissions along with other chemical emissions.[13] Formaldehyde, toluene, and limonene are a few of the most common VOCs that are emitted by consumer products such as cleaning solvents, paints, and printers in an indoor environment.[14] Trees are also an important biological source of VOC; it is known that they emit large amounts of VOCs, especially isoprene and terpenes. Another significant source of VOC emission is crude oil tanking. Both during offloading and loading of crude oil tankers VOC are released to the atmosphere. Lately, there has been an environmental focus on this issue resulting in improved VOC handling on newer tankers, and crude oil loading terminals.
Since people today spend approximately 80%, if not more of their time at home or in an office, long-term exposure to VOCs in the indoor environment can contribute to sick building syndrome (SBS).[15] Many building materials such as paints, adhesives, wall boards, and ceiling tiles emit formaldehyde, which irritates the mucous membranes and can make a person irritated and uncomfortable.[16] There are also many sources of VOCs in office buildings, which include new furnishings, wall coverings, and office equipments such as photocopy machines which can off-gas VOC particles into the air.[16]
The exhaled human breath contains few hundreds of volatile organic compounds and is used in breath analysis to serve as a VOC biomarker to test for diseases such as lung cancer.[17] One study has shown that “volatile organic compounds … are mainly blood borne and therefore enable monitoring of different processes in the body.”[18] And it appears that VOC compounds in the body “may be either produced by metabolic processes or inhaled/absorbed from exogenous sources” such as environmental tobacco smoke.[19][20] Research is still in the process to determine whether VOCs in the body are contributed by cellular processes.
Also many VOCs are found in brownfield sites.[21]
[edit] Environment
VOCs are sometimes accidentally released into the environment, where they can damage soil and groundwater. Vapors of VOCs escaping into the ambient air contribute to indoor air pollution and outdoor air pollution.
VOCs are an important outdoor air pollutant. In this field they are often divided into the separate categories of methane (CH4) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. Other hydrocarbon VOCs are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in the atmosphere, although the effect varies depending on local air quality.
[edit] Contribution to indoor air pollution
Many consumer products found around the house, such as cleaning solvents, paints, and wood preservatives from certain furniture all emit VOC compounds, which may contribute to sick building syndrome and other effects such as allergic sensitization or asthmatic symptoms.[16][22] Due to the high abundant use of VOC-containing products indoors and the high vapor pressure of VOCs, these compounds can easily off-gas into the indoor environment. They also occur in and are released from most common indoor materials from natural sources such as trees, animals, and plants as well as from synthetic sources such as petroleum derivatives.
The aromatic VOC compound benzene, emitted from exhaled cigarette smoke is labeled as carcinogenic, and is ten times higher in smokers than in nonsmokers.[16] Good ventilation and air conditioning systems are helpful at reducing VOC emissions in the indoor environment.[16] Studies also show that relative leukemia and lymphoma can increase through prolonged exposure of VOCs in the indoor environment.[23] According one review article, most of the non-methane VOC compounds are produced by plants and trees in our ecological environment.[24]
The United States Environmental Protection Agency (EPA) has found concentrations of VOCs in indoor air commonly to be 2 to 5 times greater than in outdoor air and sometimes far greater. During certain activities indoor levels of VOCs may reach 1,000 times that of the outside air.[25] Studies have shown that individual VOC emissions by themselves are not that high in an indoor environment, but the indoor total VOC (TVOC) concentrations can be up to five times higher than the VOC outdoor levels.[26] New buildings especially, contribute to the highest level of VOC off-gassing in an indoor environment because of the abundant new materials generating VOC particles at the same time in such a short time period.[27] In addition to new buildings, we also use many consumer products that emit VOC compounds, therefore the total concentration of VOC levels is much greater within the indoor environment.[28]
Relative humidity within an indoor environment can also affect the emissions of VOCs and formaldehyde. In fact, high relative humidity and high temperature allow more vaporization of formaldehyde from wood-materials and thus, can induce symptoms of sensory irritation in the eyes.[29]
Office equipment, such laser printers can emit ultrafine aerosol particles, which can contribute to ozone emission in an indoor environment.[30] There are also some chemically active VOCs, such as styrene and limonene that can react with nitrogen oxides or with ozone to produce new oxidation products and secondary aerosols, which can cause sensory irritation symptoms.[31] Although ozone is beneficial in the upper atmosphere because it absorbs UV thus protecting humans, plants, and animals from exposure to dangerous solar radiation, it poses a health threat in the lower atmosphere by causing respiratory problems. In addition, indoor ozone sources also include air-freshening devices and air-purifiers as well as large copy machines.[32] These devices can increase indoor ozone level from 6 to 453 ppb, which can induce asthmatic symptoms or increase allergic sensitization in individuals.[33]
Seasonality can affect indoor VOC levels. According to Barro (2009), it has been found that VOC concentration in an indoor environment is the highest during the winter, which is three to four times higher than the VOC concentrations during the summer.[34] And the possible reasons for high indoor VOC levels are due to the low air exchange rates between the indoor and outdoor environment as a result of tight-shut windows and the increasing use of humidifiers to keep the indoor air moist.[35]
People should be aware of their indoor air quality and take alternatives to prevent the increase of indoor air pollutants. For example, volatile organic compounds can have health affects on infants or very young children. It has been reported that “respiratory, allergic, or immune effects in infants or children” are associated with indoor VOCs and other indoor air pollutants.[36] It is suggested that VOC particles in an indoor environment can be reduced by 50% when household rugs and carpets are cleaned with efficient vacuum cleaners and hot water.[37]
The definitions of VOCs used for control of precursors of photochemical smog used by EPA and states with their own outdoor air pollution regulations includes exemptions for compounds that are technically only those volatile organic compounds but that are determined to be non-reactive or of low-reactivity in the smog formation process. EPA formerly defined these compounds as Reactive Organic Gases (ROG) but changed the terminology to VOC for simplicity's sake. However, this specific use of the term VOCs can be misleading, specifically when applied to indoor air quality because many chemicals that are not regulated for purposes of controlling outdoor air pollution but that are important from an indoor air quality perspective are still found in products that are labeled as to VOC content according to the requirements of ambient air pollution regulation.
In recent years many common materials and products used indoors have been developed and are labeled by their manufacturers as "low VOC" or "zero VOC content" and other similar terms. While some of these products may actually have low VOC content in the broader definition of VOC relevant to indoor air, some products so labeled may actually have larger VOC content but the VOCs contained in them may be exempt from the EPA's definition. For more information on VOCs, visit EPA's indoor air quality web pages at http://www.epa.gov/iaq/voc.html.
[edit] See also
[edit] References
- ^ [1]
- ^ "Directive 2004/42/CE of the European Parliament and of the Council" (Website.) EUR-Lex, European Union Publications Office. Retrieved on 2007-09-27.
- ^ [2]
- ^ [3]
- ^ [4]
- ^ "What are VOCs." (Website). The British Coatings Federation. Retrieved on 2007-09-03.
- ^ "VOCs" (Commercial website). ICI Paints. Retrieved on 2007-09-03.
- ^ Air Resources Board: Reactivity Background (Website). Air Resources Board, California Environmental Protection Agency. Retrieved on 2007-09-03.
- ^ "ESPERE Climate Encyclopedia." (Website.) Atmospheric Chemistry Department, Max Planck Institute for Chemistry. "Industry" section. Retrieved on 2007-09-26.
- ^ About EPA's Ratings
- ^ "Climate Change 2001: The Scientific Basis" Intergovernmental Panel on Climate Change (IPCC), published on United Nations Environmental Programme/GRID-Arendale website. Section 4.2.1.1: "Non-CO2 Kyoto Gases, Methane (CH4)." Retrieved on 2007-09-26.
- ^ "Background". http://www.naturalgas.org/overview/background.asp. Retrieved on 2008-01-06.
- ^ Hesterberg TW, Lapin CA, and Bunn, WB. (2008). A comparison of emissions from vehicles fueled with diesel or compressed natural gas. Environmental Science & Technology, 42(17), 6437-6445.
- ^ Bernstein, J. A., Alexis, N., Bacchus, H., Bernstein, I. L., Fritz, P., Horner, E., et al. (2008). The health effects of nonindustrial indoor air pollution. Journal of Allergy and Clinical Immunology, 121(3), 585-591. doi:10.1016/j.jaci.2007.10.045
- ^ Wang, S., Ang, H. M., & Tade, M. O. (2007). Volatile organic compounds in indoor environment and photocatalytic oxidation: State of the art. Environment International, 33(5), 694-705. "doi: 10.1016/j.envint.2007.02.011"
- ^ a b c d e Bernstein, J. A., Alexis, N., Bacchus, H., Bernstein, I. L., Fritz, P., Horner, E., et al. (2008). The health effects of nonindustrial indoor air pollution. Journal of Allergy and Clinical Immunology, 121(3), 585-591. "doi:10.1016/j.jaci.2007.10.045"
- ^ Buszewski, B., Kesy, M., Ligor, T. and Amann, A. (2007). Human exhaled air analytics: biomarkers of diseases. Biomedical Chromatography, 21(6), 553-566. "doi: 10.1002/bmc.835"
- ^ Miekisch, W., Schubert, J. K., and Noeldge-Schomburg, G. F. E. (2004). Diagnostic potential of breath analysis—focus on volatile organic compounds. Clinica Chimica Acta, 347(1-2), 25-39. Retrieved March 24, 2009 from "ScienceDirect Database"
- ^ Buszewski, B., Kesy, M., Ligor, T. and Amann, A. (2007). Human exhaled air analytics: biomarkers of diseases. Biomedical Chromatography, 21(6), 553-566. "doi: 10.1002/bmc.835"
- ^ Mazzone, P.J. (2008). Analysis of volatile organic compounds in the exhaled breath for the diagnosis of lung cancer. Journal of Thoracic Oncology. 3(7), 774-780. Retrieved Abstract on March 24 2009 from PubMed Database "PMID: 18594325"
- ^ "Brownfields Assessment Pilot Fact Sheet" (Website.) US Environmental Protection Agency Retrieved on 2000-12.
- ^ Yu, C., & Crump, D. (1998). A review of the emission of VOCs from polymeric materials used in buildings. Building and Environment, 33(6), 357-374.
- ^ Irigaray, P., Newby, J. A., Clapp, R., Hardell, L., Howard, V., Montagnier, L., et al. (2007). Lifestyle-related factors and environmental agents causing cancer: An overview. Biomedicine & Pharmacotherapy, 61(10), 640-658.
- ^ Monson, R. K., (2002). Volatile organic compound emissions from terrestrial ecosystems: A primary biological control over atmospheric chemistry. Israel Journal of Chemistry 42(1), 29 -42.
- ^ http://www.epa.gov/iaq/voc.html An Introduction to Indoor Air Quality
- ^ Jones, A. P. (1999). Indoor air quality and health. Atmospheric Environment, 33(28), 4535-4564.
- ^ Wang, S., Ang, H. M., & Tade, M. O. (2007). Volatile organic compounds in indoor environment and photocatalytic oxidation: State of the art. Environment International, 33(5), 694-705.
- ^ Wang, S., Ang, H. M., & Tade, M. O. (2007). Volatile organic compounds in indoor environment and photocatalytic oxidation: State of the art. Environment International, 33(5), 694-705.
- ^ Wolkoff, P., & Kjærgaard, S. K. (2007). The dichotomy of relative humidity on indoor air quality. Environment International, 33(6), 850-857.
- ^ Destaillats, H., Maddalena, R. L., Singer, B. C., Hodgson, A. T., & McKone, T. E. (2008) Indoor pollutants emitted by office equipment: A review of reported data and information needs. Atmospheric Environment, 42(7), 1371-1388.
- ^ Wolkoff, P., Wilkins, C. K., Clausen, P. A., & Nielsen, G. D. (2006). Organic compounds in office environments – sensory irritation, odor, measurements and the role of reactive chemistry. Indoor Air, 16(1), 7-19.
- ^ Diette G.B., McCormack M.C., Hansel N.N., et al. (2008). Environmental issues in managing asthma. Respiratory Care, 53(5), 602-615.
- ^ Bernstein, J. A., Alexis, N., Bacchus, H., Bernstein, I. L., Fritz, P., Horner, E., et al. (2008). The health effects of nonindustrial indoor air pollution. Journal of Allergy and Clinical Immunology, 121(3), 585-591.
- ^ Barro, R., Regueiro, J., Llompart, M., & Garcia-Jares, C. (2009). Analysis of industrial contaminants in indoor air: Part 1. volatile organic compounds, carbonyl compounds, polycyclic aromatic hydrocarbons and polychlorinated biphenyls. Journal of Chromatography A, 1216(3), 540-566.
- ^ Schlink, U., Rehwagen, M., Damm, M., Richter, M., et al. (2004) Seasonal cycle of indoor-VOCs: comparison of apartments and cities. Atmospheric. Environment, 38, 1181-1190.
- ^ Mendell, M. J. (2007). Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: A review. Indoor Air, 17(4), 259-277.
- ^ Roberts, J. W. and Dickey, P. (1995). Exposure of children to pollutants in house dust and indoor air. Reviews of Environmental Contamination and Toxicology, 143, 59-78.
[edit] External links
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