H. Westberg

Isoprene emission fluxes determined by an atmospheric tracer technique

Abstract Sulfur hexafluoride tracer was used in a series of experiments to simulate isoprene emissions from an isolated oak grove. The measured tracer release rate and ambient concentrations of isoprene and SF 6 observed along downwind sample lines were combined to determine the mass flux of isoprene from the forest. The fluxes determined from the tracer data increased exponentially with temperature and were in close agreement with estimates determined from emission rates measured in a series of branch enclosure samples. The results of this field study demonstrate the feasibility and usefulness of simulating forest emissions as a tool for investigating turbulent transport in forested areas. Isoprene emission fluxes that can be applied in regional models are reported.

Measurement of Biogenic Sulfur Emissions from Soils and Vegetation: Application of Dynamic Enclosure Methods with Natusch Filter and GC/FPD Analysis

Emission rates of reduced sulfur gases from vegetation and soils were measured in various regions of the United States during the summer of 1985. The predominant sulfur gases emitted were hydrogen sulfide, carbonyl sulfide and dimethylsulfide. Typically, vegetative (forests, crops, etc.) emission fluxes varied between approximately 10 and 60 ng S m-2 min-1. Biogenic sulfur fluxes from mollisol and histisol soils averaged 15 and 217 ng S m-2 min-1, respectively. Salt water marsh fluxes with a geometric mean of 293 ng S m-2 min-1 were the highest measured. These biogenic sulfur fluxes are somewhat lower than those measured during the SURE study at some of the same sites. The natural sulfur emission fluxes reported herein together with those data included in the two accompanying manuscripts provide the basis for developing a national inventory of reduced sulfur emissions from soils, crops and trees. When combined these data also will provide a foundation for deriving uncertainty limits associated with these flux estimates.

Application of Atmospheric Tracer Techniques for Determining Biogenic Hydrocarbon Fluxes from an Oak Forest

Sulfur hexafluoride tracer was used in a series of experiments to simulate isoprene emissions from an isolated oak forest. The measured tracer release rate and ambient concentrations of isoprene and SF6 observed along a downwind sample line were combined to determine the mass flux of isoprene from the forest. Results based only upon the maximum isoprene and SF6 concentrations observed along the downwind sample line were in good agreement with fluxes calculated from the crosswind concentration integrals of isoprene and SF6. The fluxes determined from the tracer data increased exponentially with temperature and were in close agreement with estimates determined from emission rates measured in a series of branch enclosure samples collected in the forest and a biomass factor taken at the midpoint of a range of available biomass factors. The results of this field study demonstrate the feasibility and usefulness of simulating forest emissions as a tool for investigating turbulent transport in forested areas.