Assessing the backward Lagrangian stochastic model for determining ammonia emissions using a synthetic source

The backward Lagrangian stochastic (BLS) model for estimating ammonia emissions from agricultural sources was assessed in an ammonia recovery experiment. The open-path tunable diode laser spectrometer was used to measure atmospheric ammonia concentrations. The results indicated that the ratio of estimated to actual emission (QBLS/Q) decreased with increasing concentration measurement height, and the optimum measurement height increased as fetch (F) increased. The accuracy of QBLS was insensitive to fetch with a range of 15-60 m. The optimum ratio of concentration measurement height to fetch decreased with increasing fetch. In this study, the optimum ratio of concentration measurement height to fetch was 0.083 and 0.045 for F = 15 m and F = 30 m, respectively. It is recommended that the laser sensor should be placed as close to the source as possible to reduce concentration measurement uncertainty for measurement of ammonia emission from farmland. The wheat canopy had a significant effect on QBLS/Q when the concentration measurement height above the wheat canopy was no more than 0.38 m. The laser path should be placed at least 0.58 m above the wheat canopy to minimize the effect of wheat canopy on the accuracy of the BLS model.