Inferring the source strength of isoprene from ambient concentrations

This paper reports on the application of an inverse Lagrangian technique that uses localized near-field (LNF) theory to calculate the source strength profile of isoprene from deciduous forest canopies. The basic tenet considered in this study is that the prevailing ambient isoprene concentrations observed over forests represent the source strength of the underlying surface as the scalar is transported from the sites of biosynthesis to the measurement point above forest canopies. Using information on the distribution of active isoprene biomass and the plant canopy environment, a two-storey canopy model was developed and applied to estimate isoprene emission rate profiles for a monoculture aspen forest whose isoprene source is homogeneously distributed throughout the landscape. Modelled results show that isoprene emission rates strongly vary with canopy depth, with maximum values coinciding with canopy layers with largest amount of active biomass. The model also captures the strong diurnal patterns of isoprene emissions from the forest canopy. We conclude that the present modelling system provides a practical method for estimating isoprene emission rate profiles based on the knowledge of atmospheric turbulence and ambient concentrations.