Volatile organic compounds (
VOCs) are
organic chemical compounds that have high enough
vapor pressures under normal conditions to significantly
vaporize and enter the atmosphere.
Volatile organic compounds are numerous and varied. Although ubiquitous in nature and modern industrial society, they may also be harmful or toxic. VOCs, or subsets of the VOCs, are often
regulated.
Background
VOCs may be natural or synthetic. Like organic chemicals in general,
there are millions of 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.
Definitions
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.
Canada
Health Canada classes VOCs as organic compounds that have boiling points roughly in the range of . The emphasis is placed on commonly encountered VOCs which would have an effect on air quality.
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.
United States
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.
The
United States Department of Labor and it's Occupational Safety
and Health Administration (OSHA) regulate VOC exposure in the workplace.
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 , German , GEV testing method for the .
Overview over VOC emissions rating schemes, Healthy Buildings Conference 2009
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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:
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.
Sources
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.
Methane
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.
Formaldehyde
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.
[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. ] 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.
Importance
General Use
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).
Move "Chemical Fingerprinting" to its own article.
Chemical Fingerprinting
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:
Atmospheric
- Unspecified VOCs are important in the creation of smog.
- Tetrachloroethene use at dry cleaners and by industry.
Groundwater
- MTBE was banned in the USA around 2004 in order to prevent further contamination of drinking water aquifers.
Indoor Air
See
Indoor Air Quality The following detail should be moved to its own article
and should be referenced here and from the
Indoor air quality article.
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.
[Dales, R., Liu, L., Wheeler, A. J., ]
& Gilbert, N. L. (2008). Quality of indoor residential air and health.
CMAJ: Canadian Medical Association Journal, 179(2), 147-152. 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 ârespiratory, allergic, or immune
effects in infants or childrenâ 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. For more information on VOCs, visit EPA's indoor air
quality web pages at http://www.epa.gov/iaq/voc.html.
See also
- NMVOC (non-methane volatile organic compounds)
