The emissions and subsequent reactions in the troposphere of organic compounds from vegetation is an important contribution to chemical cycles that lead to the formation of ozone and other oxidants and of acidic species. Knowledge of the emission rates of these biogenic compounds is crucial to understanding the role of these compounds in the atmosphere and to assessing the effectiveness of control strategies based on reduction of emissions from anthropogenic sources of volatile organic compounds and oxides of nitrogen. Of these biogenic compounds, isoprene is one of the most prevalent emissions from vegetation. This project involves a closure field study of isoprene at a site in a deciduous forest of central Pennsylvania. Isoprene and its immediate oxidation products will be monitored so that diurnal concentration patterns of these species can be established. Diffusion rates of gases in and above the forest canopy for typical summertime meteorological conditions will be determined by tracer releases. Vertical profiles of the concentrations of isoprene and important photochemical reactants and of other environmental parameters will be measured from towers and tethered balloons in order to obtain a mass balance of isoprene over the forested area. The results of this study will provide an improved understanding of the fate of isoprene in the atmosphere and how this natural hydrocarbon affects key intermediates that control the levels of several chemically and radiatively important species in the troposphere.
