The emission of non-methane hydrocarbons (NMHC) from natural sources has been known for over two decades. The major source is thought to be vegetation. Other significant natural sources are marine algae, microbial activity in soils, natural gas seeps, the biomass burning. Natural hydrocarbon emissions from plants play an important role in the generation of photochemical oxidants in the troposphere, but there are a number of uncertainties in regional and global inventories of these biogenic compounds. Much of the uncertainty arises because there is a lack of precise data relating hydrocarbon emissions to key environmental variables that regulate such emissions from vegetation. In addition, there is uncertainty about the chemical identification of a large fraction of biogenic hydrocarbons, and very little is known of the physiology or biochemistry of plant hydrocarbon production. This project will conduct laboratory studies to a) measure accurately the environmental variables controlling the biogenesis of isoprene and related NMHC in plants, b) provide new, chemical identification of emitted NMHC, and c) explore the role of micro organisms on leaf surfaces as sinks or sources of NMHC. NMHC emissions form plants in environmentally controlled gas exchange chambers will be characterized by gas chromatography measurements, with identification of hydrocarbons by gas chromatography/mass spectrometry. By using plants representing major plant groups and ecosystems, NMHC emissions will be related to air temperature, light intensity, humidity, and carbon dioxide concentration, and algorithms relating emissions to these parameters will be developed. A model will be developed to explain how and why plants emit isoprene and related NMHC, and to suggest the environmental regulation of such emissions.
