Author
 |
Harper, Lowry |
|
Submitted to: National Atmospheric Deposition Program's Ammonia Workshop
Publication Type: Proceedings Publication Acceptance Date: 10/22/2003 Publication Date: 10/22/2003 Citation: Harper, L.A. 2003.0Measurement techniques and models for ammonia emissions at the farm level. National Atmospheric Deposition Program's Ammonia Workshop. p. 129. Interpretive Summary: Ammonia is the only significant basic atmospheric gas which neutralizes acid gases produced by the combustion of fossil fuels. This neutralization process creates an aerosol which produces haze and possible health effects. Ammonia is emitted from some agricultural operations but it has unique chemical and physical properties which make it is difficult to obtain accurate concentrations and to determine representative emission rates. Ammonia emissions are driven by chemical and physical factors that should not be affected during the measurement process. If these factors are subject to interference, the resulting information will be non-representative concentration measurements and emissions determinations. Scientists at the USDA-ARS, J. Phil Campbell Sr., Natural Resources Conservation Center, Watkinsville, GA, have developed mathematical relationships and have made field measurements of the effects of these factors and have shown problems associated with the influence of measurement techniques. Methods of measurement that do not change the critical chemical and physical factors influencing ammonia emissions are known as non-interference techniques. Non-interference techniques should be used in determination of emissions; however, use of inappropriate, non-interference techniques will also give erroneous results. We made comparisons of emissions determinations using both appropriate and inappropriate measurement technologies. These methods of estimating emissions showed large differences in emissions rates. Available statistical emissions models showed good fit to data but only over a limited geographical area. An alternative fundamental model produced slightly poorer predictions but works over a broad geographical area. Reliable data on trace gas emissions, evaluated from measurement or from models, are needed so that decisions may be made by other scientists, designers, managers, and regulators on sound, scientifically-based information. Technical Abstract: The unique chemical and physical properties of ammonia make it difficult to obtain accurate atmospheric measurements of concentrations and to determine representative emission rates. Ammonia is a diffusive gas and emissions are driven by the chemical and physical factors of solution concentration, solution hydrogen ion concentration (pH), solution temperature, and ambient air turbulence (represented by windspeed). Influencing these factors during measurement results in non-representative estimates of concentrations and emissions. Mathematical relationships and field measurements of the effects of these factors have shown the problems associated with measurement influence. Non-interference techniques should be used in determination of emissions and for the verification of models; however, use of inappropriate, non-interference techniques will also give erroneous results. We made comparisons of emissions using appropriate and inappropriate measurement technologies. Large differences were obtained in emissions rates. Available statistical emissions models showed good fit to data although the geographical extent of usefulness was limited. A process model had slightly poorer fit to data but was not geographically limited. |
