Applications and theory of micrometeorological flux measurement
Several aspects of micrometeorological flux measurement are explored in this thesis. After a brief sketch of the history of the topic, the field testing of a tunable diode laser trace gas analyzer system (TDLTGAS) is reported. This system uses infrared absorption spectroscopy to monitor atmospheric ammonia concentrations. We monitored ammonia concentration gradients over 3 plots receiving different manure applications. From the gradients, fluxes of ammonia were calculated every 15 min, allowing continuous monitoring of the three treatments. The system functioned well and analysis of the response showed no problems with ammonia adsorption to the walls of the system. A technique for monitoring flux ratios from small (<5 m2) microplots was also field tested. This method monitors concentration profiles close to the surface, and from these the ratio of gradients, which is equal to the ratio of fluxes, is calculated. The field test of this method used acetylene inhibition of denitrification. Acetylene prevents the reduction of N2O to N2 by denitrifying bacteria, thereby increasing the flux of N2O by an amount equal to the N2 flux that would have been. By comparing the ratio of N2O fluxes from microplots with and without acetylene, an estimate of N2 production by denitrification was obtained. Field testing showed the technique to be practical and easily implemented. The final chapter of this thesis analyzes the relationship between a canopy scalar source profile and the resulting concentration profile. The model developed here translates the temporal near-field into a spatial near-field, allowing a concentration profile to be calculated from a source distribution through a mixing matrix. The mixing matrix sums up the contribution of each source to the gradient at each height, and the gradient profile is then integrated to determine the concentration profile. Comparison of the model with a wind tunnel dispersion experiment shows excellent agreement, though field testing of the model is still required.