Title: Accuracy of lagoon gas emissions using an inverse dispersion method Authors
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 12, 2012
Publication Date: June 10, 2012
Citation: Ro, K.S., Johnson, M.H., Stone, K.C., Hunt, P.G., Todd, R.W., Flesch, T. 2012. Accuracy of lagoon gas emissions using an inverse dispersion method. In: Proceedings of the International Symposium on Emissions of Gas and Dust from Livestock, June 10-12, 2012, Saint-Malo, France. Interpretive Summary: Measuring gas emissions from animal waste treatment lagoons is challenging because these settings are not ideal for existing micrometeorological gas measuring techniques. This study investigates the optimal location of wind and concentration sensors in an animal waste treatment lagoon environment that produces the most accurate emission measurements. A fabricated floating emission source with known emission is used to determine the accuracy of the inverse-dispersion technique. Although a lagoon environment is challenging and clearly violates some of the assumptions made in the technique development, our results at this study lagoon shows a reasonably high overall accuracy level of 77%. The accuracy improves to 99% when the wind sensor is placed on the upwind berm and the concentration sensor is placed on the downwind berm. This suggests that the inverse-dispersion technique can be used to accurately measure lagoon emissions with the sensors placed on the berm.
Technical Abstract: Measuring gas emissions from treatment lagoons and storage ponds poses challenging conditions for existing micrometeorological techniques because of non-ideal wind conditions. These include those induced by trees and crops surrounding the lagoons, and lagoons with dimensions too small to establish equilibrated microclimate conditions within the water boundary. Using a synthetic floating emission source with known emission rates from an irrigation pond, this study evaluated the accuracy of an emerging backward Lagrangian stochastic (bLS) inverse-dispersion technique to measure lagoon emissions. The measured parameters were wind statistics and path-integrated concentrations (PICs) from multiple locations. Anemometers were located on the upwind, downwind, side berm parallel to wind, or directly above pond water surface. PICs were monitored within the pond and on the downwind berm. Additionally, the berm surface was deliberately roughened during the summer by placing pine straw bales along the berms to simulate vegetation growth. The accuracy of the inverse-dispersion technique was significantly affected by the location of the three-dimensional sonic anemometers. Generally using an anemometer located on the berm produced the more accurate results than using an anemometer located directly above water surface. The total average accuracy of all combinations of anemometer location and PICs for both smooth and rough berm surface conditions was 0.77 ± 0.23 (N = 398). This lagoon study showed an accuracy level not very different from environments that meet the ideal assumptions of the inverse-dispersion model, thus, demonstrating the robustness of the inverse-dispersion technique even in non-ideal settings.