Volatile Organic Compound
Volatile Organic Compound (source wikipedia)
VOCs may be natural or synthetic. Like organic chemicals in general, there are many different compounds which may be classified as VOCs. The compounds the nose detects as smells are generally VOCs. Modern industrial chemicals such as fuels, solvents, coatings, feedstocks, and refrigerants are usually VOCs.
As organic chemicals, VOC may have health consequences, but this is depending on the specific chemicals that are part of the umbrella definition “VOC”. For indoor air purposes, there are long lists of limit values published by German AgBB, French AFSSET, and California EPA (“CREL”). Because they tend toward the gaseous state, management of toxic VOCs is more difficult than with non-volatile compounds. Human exposure to VOCs can be through contact with the solid, liquid, or gaseous forms, inhalation of the gaseous form, or ingestion of the liquid form or solutions containing the VOC.
Because of their health effects, VOCs are regulated in some places. The large number of VOCs combined with their numerous exposure pathways make comprehensive management, discussion or regulation of volatile organic compounds impractical. Instead, subsets of VOCs are regulated by a wide variety of governmental agencies.
There is no clear and widely supported definition of a VOC. 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. Laws or regulations are often responsible for creation of legal definitions of VOCs or definitions of subclasses of VOCs.
Health Canada classes VOCs as organic compounds that have boiling points roughly in the range of 50 to 250 °C (122 to 482 °F). The emphasis is placed on commonly encountered VOCs which would have an effect on air quality.
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.
VOCs (or specific subsets of the VOCs) are legally defined in the various laws and codes under which they are regulated. Other definitions may be found from government agencies investigating or advising about VOCs.
The United States Environmental Protection Agency regulates VOCs in the air, water, and land. The Safe Drinking Water Act implementation even includes a short list labeled VOCs in connection with contaminants which are organic and volatile. The EPA also publishes testing methods for chemical compounds, some of which refer to VOCs. In addition to drinking water, VOCs are regulated in discharges to waters (sewage treatment and stormwater disposal), as hazardous waste, but not in non industrial indoor air. Volatile organic chemicals which are hazardous material would be regulated by the Pipeline and Hazardous Materials Safety Administration while being transported.
Indoor air quality and emissions into indoor air
In most countries a separate definition of VOCs is used with regard to indoor air quality that comprises each organic chemical compound that can be measured as follows: Adsorption from air on Tenax TA, thermal desorption, gas chromatographic separation over a 100% non polar column (dimethylpolysiloxane). VOC (volatile organic compounds) are all compounds that appear in the gas chromatogram between and including n-hexane and n-hexadecane. Compounds appearing earlier are called VVOC (very volatile organic compounds) compounds appearing later are called SVOC (semi-volatile organic compounds). See also these standards: ISO 16000-6, ISO 13999-2, VDI 4300-6, German AgBB evaluating scheme, German DIBt approval scheme, GEV testing method for the EMICODE. Overview over VOC emissions rating schemes, Healthy Buildings Conference 2009.
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. 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:
|0% ≤ VOC content ≤ 0.29%
|0.3% ≤ VOC content ≤ 7.99%
|8% ≤ VOC content ≤ 24.99%
|25% ≤ VOC content ≤ 50%
|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.
Volatile organic compounds are produced naturally through biological mechanisms such as metabolism. Industrial use of fossil fuels produces VOCs either directly as products (e.g. gasoline) or indirectly as byproducts (e.g. automobile exhaust).
Some examples of VOC sources follow.
The most common VOC is methane, a greenhouse gas sometimes excluded from analysis of other VOCs using the term non-methane VOCs, or NMVOCs.
Major worldwide sources of atmospheric methane include wetlands ruminants such as cows, energy use, rice agriculture, landfills, and burning biomass such as wood. Methane is the primary component of natural gas.
Since people today spend most of their time at home or in an office, long-term exposure to VOCs in the indoor environment can contribute to sick building syndrome. 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. There are also many sources of VOCs in office buildings, which include new furnishings, wall coverings, and office equipment such as photocopy machines which can off-gas VOCs into the air.
Volatile organic compounds are useful as
- The wide range of VOCs allows organic materials or processes to be identified by combinations of VOCs they may contain (or, especially, emit to the atmosphere).
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. One study has shown that “volatile organic compounds … are mainly blood borne and therefore enable monitoring of different processes in the body. 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. Research is still in the process to determine whether VOCs in the body are contributed by cellular processes or by the cancerous tumors in the lung or other organs.
Environment and health
Releases, intentional or not, of VOCs may affect the environment or human health, depending on the particular chemicals involved, the quantities and concentrations, and the relative locations of “receptors” which are sensitive to the particular chemical.
Some examples of VOCs causing health or environmental effects follow:
- Methane, a VOC, is an important greenhouse gas.
- Unspecified VOCs are important in the creation of smog.
- Chlorofluorocarbons were banned or regulated because of possible damage to the ozone layer from these compounds.
- Tetrachloroethene use at dry cleaners and by industry.
- MTBE was banned in the USA around 2004 in order to prevent further contamination of drinking water aquifers.
Indoor air Indoor air quality
Because modern homes are fairly well sealed, airborne contaminants released within such homes dissipate much slower than in “leaky” homes or than the contaminants would dissipate outdoors.
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. 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. Good ventilation and air conditioning systems are helpful at reducing VOC emissions in the indoor environment. Studies also show that relative leukemia and lymphoma can increase through prolonged exposure of VOCs in the indoor environment. According one review article, most of the non-methane VOC compounds are produced by plants and trees in our ecological environment.
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. 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. 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. 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.
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. Office equipment, such laser printers can emit ultrafine aerosol particles, which can contribute to ozone emission in an indoor environment. 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. 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. These devices can increase indoor ozone level from 6 to 453 ppb, which can induce asthmatic symptoms or increase allergic sensitization in individuals.
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. 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.
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. 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.
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.
Emissions of VOCs from products into indoor air are limited by some regulations in some countries (especially in France and in Germany), by many ecolabels, and by some sustainable buildings design standards. Even though these VOC rating schemes are describing the same issue, the specifications and the testing protocols differ by country and by label. An attempt to promote harmonization of such rating schemes was a specialized workshop during Healthy Buildings Conference 2009 in Syracuse NY (USA).