Forest Hydrocarbon Emissions: Relationships Between Fluxes and Ambient Concentrations

Abstract

In recent years there has been growing interest in natural hydrocarbon emissions from trees and other foliage. It is known that, if transported to urban areas, natural hydrocarbon emissions can add to man-made ozone and haze. Whether the contribution of natural emissions is important depends on a large number of factors such as the specific hydrocarbons emitted by plants, the magnitude of the emission rates, the distribution of tree species, and meteorological and climatic conditions. The purpose of this study was to determine which specific hydrocarbons are emitted by trees and the ambient levels of these hydrocarbons near the forest. The scope of the study was limited to a dozen species of trees in the forested areas near Baton Rouge, Louisiana, but more than a hundred gases were measured in each sample. The authors found that: (1) only 5 or 6 hydrocarbons constitute 90 percent of the emissions, in which isoprene is one of the largest components when it is emitted; (2) although about 20 hydrocarbons are emitted from the trees were studied, surprisingly, only eight were found in the forest atmosphere, some only occasionally and at very low concentrations.