This month’s Featured Molecules come from the Report from Other Journals column, Nature: Our Atmosphere in the Year of Planet Earth, and the summary found there of the paper by Lelieveld et al. (1, 2) Added to the collection are several volatile organic compounds (VOCs) that are emitted by a variety of plants. The term VOCs is a common one in environmental chemistry, and is interpreted quite broadly, typically referring to any organic molecule with a vapor pressure sufficiently high to allow for part-per-billion levels in the atmosphere. Common VOCs include methane (the most prevalent VOC), benzene and benzene derivatives, chlorinated hydrocarbons, and many others. The source may be natural, as in the case of the plant emissions, or anthropogenic, as in the case of a molecule such as the gasoline additive methyl tert-butyl ether (MTBE).
The oxidation of isoprene in the atmosphere has been a source of interest for many years. Several primary oxidation products are included in the molecule collection, although a number of isomeric forms are also possible (3).
Methyl tert-butyl ether, MTBE, is used as an additive in unleaded gasoline to raise the octane number. Its use has declined in the United States in response to environmental and health concerns.
Isoprene, 2-methyl-1,3-butadiene, is an example of a volatile organic compound emitted by forests.
The area of VOCs provides innumerable topics for students’ research papers and projects at all levels of the curriculum from high-school chemistry through the undergraduate courses in chemistry and environmental science. Along the way students have the opportunity for exposure to fields such as epidemiology and toxicology, that may be new to them, but are of increasing importance in the environmental sciences. The MTBE story is an interesting one for students to discover, as it once again emphasizes the role that unintended consequences play in life. An exploration of the sources, structures, reactivity, health and environmental effects and ultimate fate of various VOCs reinforces in students’ minds just how interconnected the chemistry of the environment is, a lesson that bears repeating frequently.
Lelieveld, J.; Butler, T. M.; Crowley, J. N.; Dillon, T. J.; Fischer, H.; Ganzeveld, L.; Harder, H.; Lawrence, M. G.; Martinez, M. ; Taraborrelli, D.; Williams, J. Nature, 2008, 452, 737–740.
Kroll, Jesse H.; Ng, Nga L.; Murphy, Shane M.; Flagan, Richard C.; Seinfeld, John H. Environ. Sci. Technol. 2006, 40, 1869–1877.
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