Title: Optimal sensor locations for the backward Lagrangian stochastic technique in measuring lagoon gas emission Authors
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 23, 2013
Publication Date: N/A
Interpretive Summary: As a result of biochemical transformation of manures, anaerobic waste lagoons and storage ponds from concentrated animal feeding operations (CAFOs) are sources for odor, ammonia, and greenhouse gas emissions. Accurate assessment of these gas emissions from waste lagoons and storage ponds is very important for proper planning and management of animal wastes. Yet, the actual measurement of these gas emissions is challenging because they are typically located in non-ideal locations surrounded by trees and crops. Our previous work indicated that the inverse dispersion technique may become a potentially useful tool to measure lagoon gas emission. This paper reports the results of a study that has significantly expanded the scope of our previous work via a much larger number of datasets (from 104 to 838 datasets) with gas concentration data and wind statistics obtained from various locations of lagoon landscape. It develops a set of “rules” to help users identify good and poor locations for wind and concentration sensors within the lagoon boundary. Considering the practical difficulties in setting up equipment and the accuracies associated with various sensor locations, we recommend both wind and concentration sensors be set on the downwind berm.
Technical Abstract: This study evaluated the impact of gas concentration and wind sensor locations on the accuracy of the backward Lagrangian stochastic inverse-dispersion technique (bLS) for measuring gas emission rates from a typical lagoon environment. Path-integrated concentrations (PICs) and 3-dimensional (3D) wind vector data were collected at different locations within the lagoon landscape. A floating 45 meter x 45 meter perforated pipe network on an irrigation pond was used as a synthetic distributed emission source for the controlled release of methane. Numerous 15-minute datasets (838) were collected under different atmospheric stability and berm surface conditions over a two year period. The PIC location had a significant impact on the accuracy of the bLS technique. The PIC located on downwind berm consistently yield the best bLS accuracy with the 3D sonic anemometer located on upwind, side, or downwind berm (accuracies ranging from 78 to 109%). The location of the 3D sonic anemometer was generally not a factor for the measured accuracies with the PIC positioned on the downwind berm. The middle PICs consistently produced the lowest accuracy with any 3D anemometer locations (< 68% accuracy). The accuracy of the emission measurements with this sensor setting was statistically similar to that found in more ideal homogeneous terrain conditions. Considering the practical difficulties in setting up equipment and the accuracies associated with various sensor locations, we recommend both wind and concentration sensors be set on the downwind berm.