Volatile organic compounds are organic chemicals that have a high vapor pressure at ordinary
room temperature. Their high vapor pressure results from a low boiling point, which causes
large numbers of molecules to evaporate or sublimate from the liquid or solid form of
the compound and enter the surrounding air. For example, formaldehyde, which evaporates
from paint, has a boiling point of only –19 °C. VOCs are numerous, varied, and ubiquitous.
They include both human-made and naturally occurring chemical compounds. Most scents
or odours are of VOCs. VOCs play an important role in communication between plants, and
messages from plants to animals. Some VOCs are dangerous to human health or cause harm
to the environment. Anthropogenic VOCs are regulated by law, especially indoors, where
concentrations are the highest. Harmful VOCs typically are not acutely toxic, but have
compounding long-term health effects. Because the concentrations are usually low and the
symptoms slow to develop, research into VOCs and their effects is difficult.
Definitions Diverse definitions of the term VOC are in
use. The definitions of VOCs used for control of
precursors of photochemical smog used by the EPA, and states in the US with independent
outdoor air pollution regulations include exemptions for VOCs 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 but changed the terminology to VOC.
In the USA, different regulations vary between states - most prominent is the VOC regulation
by SCAQMD and by the California Air Resources Board. However, this specific use of the term
VOCs can be misleading, especially when applied to indoor air quality because many chemicals
that are not regulated as outdoor air pollution can still be important for indoor air pollution.
Canada Health Canada classes VOCs as organic compounds
that have boiling points roughly in the range of 50 to 250 °C. The emphasis is placed
on commonly encountered VOCs that 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.
US 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
includes a list labeled "VOCs in connection with contaminants that 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, as hazardous waste, but not in non industrial indoor air. The
United States Department of Labor and its Occupational Safety and Health Administration
regulate VOC exposure in the workplace. Volatile organic compounds that are hazardous material
would be regulated by the Pipeline and Hazardous Materials Safety Administration while being
transported. Biologically generated VOCs
Not counting methane, biological sources emit an estimated 1150 teragrams of carbon per
year in the form of VOCs. The majority of VOCs are produced by plants, the main compound
being isoprene. The remainder are produced by animals, microbes, and fungi, such as molds.
The strong odor emitted by many plants consists of green leaf volatiles, a subset of VOCs.
Emissions are affected by a variety of factors, such as temperature, which determines rates
of volatilization and growth, and sunlight, which determines rates of biosynthesis. Emission
occurs almost exclusively from the leaves, the stomata in particular. A major class of
VOCs is terpenes, such as myrcene. Providing a sense of scale, a forest 62,000 km2 in
area is estimated to emit 3,400,000 kilograms of terpenes on a typical August day during
the growing season. VOCs should be a factor in choosing which trees to plant in urban
areas. Induction of genes producing volatile organic compounds, and subsequent increase
in volatile terpenes has been achieved in maize using-3-Hexen-1-ol and other plant hormones.
Anthropogenic sources Anthropogenic sources emit about 142 teragrams
of carbon per year in the form of VOCs. Specific components
Paints and coatings A major source of man-made VOCs are coatings,
especially paints and protective coatings. Solvents are required to spread a protective
or decorative film. Approximately 12 billion litres of paints are produced annually. Typical
solvents are aliphatic hydrocarbons, ethyl acetate, glycol ethers, and acetone. Motivated
by cost, environmental concerns, and regulation, the paint and coating industries are increasingly
shifting toward aqueous solvents. Chlorofluorocarbons and chlorocarbons
Chlorofluorocarbons, which are banned or highly regulated, were widely used cleaning products
and refrigerants. Tetrachloroethene is used widely in dry cleaning and by industry. Industrial
use of fossil fuels produces VOCs either directly as products or indirectly as byproducts.
Benzene
One VOC that is a known human carcinogen is benzene, which is a chemical found in environmental
tobacco smoke, stored fuels, and exhaust from cars. Benzene also has natural sources such
as volcanoes and forest fires. It is frequently used to make other chemicals in the production
of plastics, resins, and synthetic fibers. Benzene evaporates into the air quickly and
the vapor of benzene is heavier than air allowing the compound to sink into low-lying areas.
Benzene has also been known to contaminate food and water and if digested can lead to
vomiting, dizziness, sleepiness, rapid heartbeat, and at high levels, even death may occur.
Methylene chloride Methylene chloride is another VOC that is
highly dangerous to human health. It can be found in adhesive removers and aerosol spray
paints and the chemical has been proven to cause cancer in animals. In the human body,
methylene chloride is converted to carbon monoxide and a person will suffer the same
symptoms as exposure to carbon monoxide. If a product that contains methylene chloride
needs to be used the best way to protect human health is to use the product outdoors. If
it must be used indoors, proper ventilation is essential to keeping exposure levels down.
Perchloroethylene Perchloroethylene is a volatile organic compound
that has been linked to causing cancer in animals. It is also suspected to cause many
of the breathing related symptoms of exposure to VOCs. Perchloroethylene is used mostly
in dry cleaning. While dry cleaners recapture perchloroethylene in the dry cleaning process
to reuse it, some environmental release is unavoidable. Studies show that people breathe
in low levels of this VOC in homes where dry-cleaned clothes are stored and while wearing dry-cleaned
clothing. MTBE
MTBE was banned in the US around 2004 in order to limit further contamination of drinking
water aquifers primarily from leaking underground gasoline storage tanks where MTBE was used
as an octane booster and oxygenated-additive. Indoor air
Since many people spend much of their time indoors, long-term exposure to VOCs in the
indoor environment can contribute to sick building syndrome. In offices, VOC results
from new furnishings, wall coverings, and office equipment such as photocopy machines,
which can off-gas VOCs into the air. Good ventilation and air-conditioning systems are
helpful at reducing VOCs in the indoor environment. Studies also show that relative leukemia and
lymphoma can increase through prolonged exposure of VOCs in the indoor environment.
There are two standardized methods for measuring VOCs, one by the National Institute for Occupational
Safety and Health and another by Occupational Safety and Health Administration. Each method
uses a single component solvent; butanol and hexane cannot be sampled, however, on the
same sample matrix using the NIOSH or OSHA method.
The aromatic VOC compound benzene, emitted from exhaled cigarette smoke is labeled as
carcinogenic, and is ten times higher in smokers than in nonsmokers.
The United States Environmental Protection Agency has found concentrations of VOCs in
indoor air 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 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.
VOC concentration in an indoor environment during winter is three to four times higher
than the VOC concentrations during the summer. High indoor VOC levels are attributed to the
low rates of air exchange between the indoor and outdoor environment as a result of tight-shut
windows and the increasing use of humidifiers. Regulation of indoor VOC emissions
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%
nonpolar column. VOC are all compounds that appear in the gas chromatogram between and
including n-hexane and n-hexadecane. Compounds appearing earlier are called VVOC compounds
appearing later are called SVOC. 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. Some overviews over VOC emissions rating schemes have been collected and compared.
France and Germany have enacted regulations to limit VOC emissions from commercial products,
and industry has developed numerous voluntary ecolabels and rating systems, such as EMICODE,
M1, Blue Angel and Indoor Air Comfort In the United States, several standards exist; California
Standard CDPH Section 01350 is the most popular one. Over the last few decades, these regulations
and standards changed the marketplace, leading to an increasing number of low-emitting products:
The leading voluntary labels report that licenses to several hundreds of low-emitting products
have been issued. Formaldehyde
Many building materials such as paints, adhesives, wall boards, and ceiling tiles slowly emit
formaldehyde, which irritates the mucous membranes and can make a person irritated and uncomfortable.
Formaldehyde emissions from wood are in the range of 0.02 – 0.04 ppm. Relative humidity
within an indoor environment can also affect the emissions of formaldehyde. High relative
humidity and high temperatures allow more vaporization of formaldehyde from wood-materials.
Health risks Respiratory, allergic, or immune effects in
infants or children are associated with man-made VOCs and other indoor or outdoor air pollutants.
Some VOCs, such as styrene and limonene, can react with nitrogen oxides or with ozone to
produce new oxidation products and secondary aerosols, which can cause sensory irritation
symptoms. Unspecified VOCs are important in the creation of smog.
Health effects include eye, nose, and throat irritation; headaches, loss of coordination,
nausea; damage to liver, kidney, and central nervous system. Some organics can cause cancer
in animals; some are suspected or known to cause cancer in humans. Key signs or symptoms
associated with exposure to VOCs include conjunctival irritation, nose and throat discomfort, headache,
allergic skin reaction, dyspnea, declines in serum cholinesterase levels, nausea, vomiting,
nose bleeding, fatigue, dizziness. The ability of organic chemicals to cause
health effects varies greatly from those that are highly toxic, to those with no known health
effects. As with other pollutants, the extent and nature of the health effect will depend
on many factors including level of exposure and length of time exposed. Eye and respiratory
tract irritation, headaches, dizziness, visual disorders, and memory impairment are among
the immediate symptoms that some people have experienced soon after exposure to some organics.
At present, not much is known about what health effects occur from the levels of organics
usually found in homes. Many organic compounds are known to cause cancer in animals; some
are suspected of causing, or are known to cause, cancer in humans.
Reducing exposure To reduce exposure to these toxins, one should
buy products that contain Low-VOCs or No VOCs. Only the quantity which will soon be needed
should be purchased, eliminating stockpiling of these chemicals. Use products with VOCs
in well ventilated areas. When designing homes and buildings, design teams can implement
the best possible ventilation plans, call for the best mechanical systems available,
and design assemblies to reduce the amount of infiltration into the building. These methods
will help improve indoor air quality, but by themselves they cannot keep a building
from becoming an unhealthy place to breathe. Limit values for VOC emissions
Limit values for VOC emissions into indoor air are published by e.g. AgBB, AFSSET, California
Department of Public Health, and others. These regulations have prompted several companies
to adapt with VOC level reductions in products that have VOCs in their formula, such Benjamin
Moore & Co. in the paint industry and Weld-On in the adhesive industry.
Chemical fingerprinting The exhaled human breath contains a few hundred
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.
VOC Sensors
VOCs in the environment or certain atmospheres can be detected based on different principles
and interactions between the organic compounds and the sensor components. There are electronic
devices that can detect ppm concentrations despite the non-selectivity. Others can predict
with reasonable accuracy the molecular structure of the volatile organic compounds in the environment
or enclosed atmospheres and could be used as accurate monitors of the Chemical Fingerprint
and further as health monitoring devices. Solid-phase microextraction techniques are
used to collect VOCs at low concentrations for analysis.
See also Aroma compound
Criteria air contaminants Dutch standards
Fugitive emissions NMVOC
NoVOC Organic compound
Photochemical smog Volatility
NTA Inc VOC Testing Laboratory Volatile Organic Compounds Protocol
Ozone References
External links Volatile Organic Compounds web site of the
Chemicals Control Branch of Environment Canada An Introduction to Indoor Air Quality, US
EPA website VOC in paints, finishes and adhesives
VOC emissions testing EPA NE: Ground-level Ozone Information
emission from crude oil tankers VOC emissions and calculations
VOCs, ozone and air pollution information from the American Lung Association of New
England VOC Tests
Post doc in Volatile organic compound in Food VOC emissions from printing processes, European
legislation and biological treatment Examples of product labels with low VOC emission
criteria Information about VOCs in Drinking Water
Formaldehyde and VOCs in Indoor Air Quality Determinations by GC/MS