In summary, VOCs are organic molecules that can easily be found in gaseous environments. Let s see what are the main categories of molecules that respect the definition given. What are the classes of compounds that characterize VOCs? Before to distinguish the different types of molecules that characterize VOCs, it is useful to note that these molecules can come from natural sources (biogenic origin), human processes (
anthropogenic origin ), or from both sources. are derived from vegetables. These include methane (resulting from an anaerobic decomposition process of organic substrates), a class of unsaturated hydrocarbons called terpenes and other classes of organic compounds (such as esters, aldehydes, ketones and peroxides ). instead, come mainly from industrial processes and products. This is the category of greatest interest for us so let us examine it in more detail. Among the VOCs produced by human processes we can include: Aliphatic hydrocarbons: They are chemical species containing carbon and hydrogen, linked together by single bonds only. They constitute a significant fraction of oil and are used extensively in the field of fuels. Alkenes: a kind of hydrocarbon containing double bonds. They derived from production processes of the petrochemical industry and are very important intermediate for the synthesis of many compounds. Aromatic hydrocarbons: They are very stable molecules used in many processes and products (paints, varnishes, glues, lacquers. ) Aldehydes: They are the molecules partially oxidized, widely used in the chemical and agricultural sector (fungicides, insulation, germicides, resins, disinfectants. ) Alcohols: are widely used as solvents or as intermediates in the chemical processes of high importance.
Lately they are covering an increasingly part of automotive fuels. Ethers: They are used in specific contexts, where they can be found as air contaminants. For example, THF (tetrahydrofuran) is used as an industrial solvent, while the MTBE (methyl-tertbutil-ether) is widely used as anti-knock in green gasoline. Halogenated organic compounds: In industrial applications are used a large quantities of halogen derivatives, both aliphatic and aromatic. Compounds are typically volatile, hydrophobic and toxic, and are widely used as pesticides and refrigerants. Organic sulfur compounds: the majority of these compounds do not constitute a serious problem for the environment, but at the local level can be harmful. Human activity produces them through the treatment of animal waste, water sewage and in oil refining processes. Organic nitrogenous compounds: This class covers a large number of chemical species (amines, amides, nitriles. ) which are used in a wide range of areas. Among these, there are the production of dyes, pharmaceutical chemistry, photography and What effect do they have? Now that we have developed a greater awareness of what are VOCs and what classes of molecules characterized it, it is useful to analyze the possible effects within the atmosphere.
Volatile organic compounds ( VOCs ) are – specifically – that are classified as a as they produce undesirable effects in the. The are defined as because they evaporate quickly and easily into the air. They react with in the air to form, another harmful pollutant, and they also contribute to the formation of secondary. VOCs occur in many forms and are emitted from both human sources, such as, and natural sources, such as trees and plants. Although natural sources account for about 85% of the VOCs in the air, the more reactive and therefore concerning ones are those produced by human activities. Especially in cities where there less plants, the dominant emissions of VOCs come from sources. These compounds play a key role in the formation of ozone and, which are very harmful for human health. Visit the UC Davis ChemWiki to see how VOCs contribute to smog by the production of ozone. VOCs occur in many forms (some more harmful than others) and different sources emit different forms. Such sources include use, trash incineration, and evaporation of industrial. alone contains almost 100 different hydrocarbons including, and. A major contributor to VOCs is the evaporation of various hydrocarbon-rich liquids such as gasoline from car tanks or refueling stations, industrial solvents such as oil-based paint, barbecue starter fluid, and cleaning products. As stated before, VOC emissions from vegetation is more than 5 times that of human sources (in Canada, as a whole).
However this number greatly decreases towards large cities, until it is human sources accounting for most of the harmful hydrocarbons. In densely populated cities such as Los Angeles or Mexico City the smog produced in part by VOCs has become a major problem, and the associated with it are increasingly worrisome. The emissions of volatile organic compounds has diminished in recent years due to public awareness and improved regulation. Many gasoline stations use vapor-recovery systems to minimize the VOCs emitted from the pumping of gas. Every new vehicle sold is also equipped with a, which chemically alter harmful VOCs and into less harmful pollutants. Many scientists also suggest to pump gasoline at night to reduce the amount of VOCs that can react with. The data visualization below shows a recent decrease in VOC levels in Canada. It can also be altered to view various other pollutants, most of which have been declining as well. For a more in-depth look at pollution data, including a graph showing where VOC emissions come from primarily, click. \”EWM paint 2007\” by Tom Murphy VII. Licensed under Public Domain via Wikimedia Commons – Prepared for Pollution Probe by Olivia Nugent. 2002. The Smog Primer. R. A. Hinrichs and M. Kleinbach, \”Hydrocarbons or Volatile Organic Compounds,\” in Energy: Its Use and the Environment, 5th ed. Toronto, Ont. Canada: Brooks/Cole, 2013, ch. 8, sec. C, pp. 247-250 UC Davis ChemiWiki. (Accessed July 29, 2015). Smog [Online], Available: