Estimates of volatile hydrocarbon emissions to the atmosphere indicate that biogenic sources are much greater on a global basis than anthropogenic sources. Many assumptions inherent in these estimates, however, introduce a large degree of uncertainty about both inventories. A critical review of the literature reveals nonmethane hydrocarbons in rural and remote areas consist mainly of anthropogenic species, and are composed of less than 10% biogenically-related compounds (i.e., monoterpenes and isoprene). Despite these results, some investigators continue to invoke 'natural hydrocarbon emissions' to explain naturally occurring haze, incorrectly identified gas chromatographic peaks, and high concentrations of total nonmethane hydrocarbons that are measured by indiscriminate (total hydrocarbon-methane) analyzers. In response to the suggestion that biogenic emissions are responsible for the high hydrocarbon concentrations described in several reports, the Environmental Sciences Research Laboratory of the U.S. Environmental Protection Agency initiated short-term sampling as a means of validation. A limited number of whole-air samples were collected in Tedlar bags and analyzed by gas chromatography with flame ionization detection. The areas of study included: Tulsa, Oklahoma; Rio Blanco County, Colorado; and the Great Smoky Mountains in Tennessee. Although the tests were of short duration, the results suggest monoterpenes and isoprene constitute minor components of rural air relative to anthropogenic hydrocarbons.

"January 1980."