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This fact file will provide a technical overview of volatile organic compounds (VOCs). VOCs are compounds that have a high vapor pressure and low water solubility. VOCs are of concern as indoor air pollutants and as outdoor air pollutants. However, the emphasis of that concern outdoors is different from indoors. The main concern indoors is the potential for VOCs to adversely impact the health of people that are exposed. While VOCs can also be a health concern outdoors, Environmental Protection Agency (EPA) regulates VOCs outdoors mainly because of their ability to create photochemical smog under certain conditions.
In the United States, emissions of VOCs to the outdoors are regulated by EPA mostly to prevent the formation of ozone, a constituent of photochemical smog. Many VOCs form ground-level ozone by “reacting” with sources of oxygen molecules such as nitrogen oxides (NOx), and carbon monoxide (CO) in the atmosphere in the presence of sunlight. However, only some VOCs are considered “reactive” enough to be of concern. VOCs that are non-reactive or of negligible reactivity to form ozone under these conditions are exempted from the definition of VOCs used by EPA in its regulation. Since first establishing the list of exempt compounds in 1977, EPA has added several to the list, and frequently has several petitions for additional compounds undergoing review. In addition, some states have their own definitions and lists of exempted compounds. Thus, for regulatory purposes, the specific definition of VOCs outdoors can change by what is excluded from that definition.
VOCs are sometimes categorized by the ease they will be emitted. For example, the World Health Organization (WHO) categorizes indoor organic pollutants as:
When discussing indoor environments, all organic chemical compounds that can volatize under normal indoor atmospheric conditions of temperature and pressure are VOCs. The three classifications are all important to indoor air and are all considered to fall within the broad definition of indoor volatile organic compounds. Other than volatility (or boiling point) no other criteria are used to define VOCs indoors.
Knowledge about the VOCs that are present at low concentrations in indoor air in any given situation is highly dependent on how they are measured. All available measurement methods are selective in what they can measure and quantify accurately. None can measure all VOCs that are present. For example, benzene and toluene are measured by a different method than formaldehyde and other similar compounds. The range of measurement methods and analytical instruments is large. It will determine the sensitivity of the measurements as well as their selectivity or biases. Therefore, any statement about VOCs that are present in each environment needs to be accompanied by a description of how the VOCs were measured so that the results can be interpreted correctly by a professional. In the absence of such a description, the statement would have limited practical meaning.
There are national and international programs that certify and label products and materials based on their indoor air quality impacts such as various human health and comfort effects including odor, irritation, chronic toxicity, or carcinogenicity. Such programs are likely to include consideration of at least some of the VOCs of concern for indoor air. However, the norms and requirements currently used within the product labeling and certification industry for indoor products are not standardized. The government or third-party organization has not yet established the ground rules to craft consistent, protective standard test methods to rate and compare products and materials. This lack of standardization makes it difficult for the consumer to fully understand what the labels and certifications mean in most cases. However, it is important for consumers to understand that information on labels or other product literature with broad claims about environmental impact using terms such as “green” or “environmentally friendly” may or may not include some of the VOCs emitted from the product, and therefore may not otherwise consider their adverse health effects.
“Volatile organic compounds (VOC”) are any compounds of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participate in atmospheric photochemical reactions. (Definition per 40 CFR 51.100(s))
“Volatility” refers to the property of a liquid fuel that defines its evaporation characteristics.
Reducing the concentration of VOCs indoors and outdoors is an important health and environmental goal. However, it is important to understand that there are VOCs of concern indoors and outdoors that do not impact photochemical oxidation and therefore are not regulated by EPA (42 U.S.C. 7401 et seq. (1970)). It is important to make and understand this distinction when advocating or using strategies to improve indoor air quality. For indoor air quality, ALL organic chemical compounds whose compositions give them the potential to evaporate under normal atmospheric conditions are considered VOCs and should be considered in any assessment of indoor air quality impacts.
On June 1, 2022, the EPA released the annual interactive report tracking America’s progress in controlling air pollution. “Our Nation’s Air: Trends Through 2021” offers readers an opportunity to learn about the health and environmental impacts of air pollution; track trends in air quality and emissions data, explore efforts to improve visibility in national parks; and explore community-level health impacts of air toxics emissions reported for 2017. The report shows that, between 1970 and 2021, the combined emissions of six key pollutants dropped by 78 percent. The U.S. economy remained strong – growing 292 percent over the same time. This summary tool provides access to community-level information regarding potential cancer risk and noncancer hazards from air toxics emissions. Coupled with EPA’s newly released Air Toxics Screening Assessment AirToxScreen, this tool gives communities — especially those with environmental justice concerns — more complete information about their air quality.