Atmospheric Dispersion of Ammonia During Application of Anhydrous Ammonia Fertilizer1
- O. T. Denmead,
- J. R. Freney and
- J. R. Simpson2
There is a need lo develop techniques for the prediction of the aerial spread of hazardous chemicals released in agricultural operations. The dispersion of ammonia (NH3) gas during soil injection of anhydrous NH3 is one such example. In previous work we established that after injection NH3 escaped from the soil to the atmosphere at a rate that decreased exponentially with time; in our study the whole process took about 2 h. In this paper we combine the dynamics of the emission process with existing micrometeorological theory for atmospheric dispersion from line sources, to predict NH3 concentrations in the air at the downwind edge of the field. The predictions are compared with concentrations measured during an injection operation.
Although the total NH3 emission during the operation was only 1.2 kg/ha, NH3 concentrations up to 213 µg/m3 were recorded at the downwind edge in the early stages of injection. Wind speed and atmospheric stability had large influences on NH3 dispersion. In light winds and stable conditions NH3 concentrations > 100 µg/m3 were recorded when the applicator was > 200 m upwind, and some NH3 enrichment still occurred when it was 600 m upwind.
The model underestimates NH3 concentrations when the treated width is <30 m, but predicts them very well at greater distances in both stable and unstable conditions. The model is used to predict NH3 concentrations downwind of the applicator for a range of wind speeds and emission strengths.
The approach should prove useful not only for estimating NH3 pollution hazards but also for predicting dispersion in related agricultural operations where a time-dependent decay and/or a line-source analogy are appropriate.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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