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Volatile organic compound
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Volatile organic compoundFrom Wikipedia, the free encyclopedia Jump to: navigation, search Volatile organic compounds (VOCs) 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 (–2 °F). 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, [1] 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. Contents[hide]
Definitions[edit]Diverse definitions of the term VOC[2] 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 (ROG) but changed the terminology to VOC.[citation needed] In the USA, different regulations vary between states - most prominent is the VOC regulation by SCAQMD and by the California Air Resources Board.[3] 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.
European Union[edit]A VOC is any organic compound having an initial boiling point less than or equal to 250 °C (482 °F) measured at a standard atmospheric pressure of 101.3 kPa[5] and can do damage to visual or audible senses.[citation needed] US[edit]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.[6] The United States Environmental Protection Agency (EPA) 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."[7] The EPA also publishes testing methods for chemical compounds, some of which refer to VOCs.[8] In addition to drinking water, VOCs are regulated in discharges to waters (sewage treatment and stormwater disposal), as hazardous waste,[9] but not in non industrial indoor air.[10] The United States Department of Labor and its Occupational Safety and Health Administration (OSHA) 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[edit]Not counting methane, biological sources emit an estimated 1150 teragrams of carbon per year in the form of VOCs.[11] 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.[12] Providing a sense of scale, a forest 62,000 km2 in area (the U.S. state of Pennsylvania) is estimated to emit 3,400,000 kilograms of terpenes on a typical August day during the growing season.[13] VOCs should be a factor in choosing which trees to plant in urban areas.[14] Induction of genes producing volatile organic compounds, and subsequent increase in volatile terpenes has been achieved in maize using (Z)-3-Hexen-1-ol and other plant hormones.[15] Directory: uploads uploads -> 587 Return function, r i(X) r i(0) r i(1) r i(2) r i(3) 1 0 2 4 6 Thermal Station, I 2 0 1 5 6 3 0 3 5 6 10 uploads -> Department of science and humanities department of mathematics part-a questions and answers uploads -> The Case Against the nypd’s Quota-Driven ‘Broken Windows’ Policing What Is It? uploads -> For want of a nail uploads -> Ownership Models There are two different types of ownership models uploads -> Police Militarization uploads -> City of rising star regular meting thursday, july 14, 2016 uploads -> Township of winfield uploads -> Stop Militarizing Law Enforcement Act of 2014 uploads -> The Black Panther Party’s Ten-Point Program What We Want Now! Download 190.74 Kb. Share with your friends:
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