Turbulent Schmidt number from a tracer experiment

Measurements of pesticide emission from a bare soil were used to calculate the turbulent Schmidt number (Sc): the ratio of eddy diffusivity for momentum (eddy viscosity) to the diffusivity for tracer mass. The value of Sc has implications for the measurement of trace gas emissions, and there is a broad range of reported values for the atmospheric surface layer. During our experiment Sc averaged 0.6, with large variability between observation periods. The standard deviation in Sc was 0.31, with no obvious correlation to atmospheric conditions. Some of this variability is due to measurement uncertainty, but we believe it also reflects true variability in Sc. We show that flux-gradient formula, which assume higher values of Sc, underestimate the true tracer emission rate Q. We also show that a dispersion model with Sc = 0.6, does better at inferring Q than a model with Sc = 0.45. Published by Elsevier Science B.V.