Title: Challenges in using flux chambers to measure ammonia and VOC emissions from open feedlot pen surfaces and retention ponds Authors
Submitted to: American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: March 9, 2008
Publication Date: July 11, 2008
Citation: Cole, N.A., Todd, R.W., Parker, D.B., Rhoades, M.B., Caraway, E. 2008. Challenges in using flux chambers to measure ammonia and VOC emissions from open feedlot pen surfaces and retention ponds [abstract]. Abstracts of American Dairy Science Association and American Society of Animal Science Joint Meeting, July 7-11, 2008, Indianapolis, Indiana. No. 310. 2008 CDROM. Technical Abstract: Few methodologies currently available to estimate ammonia and volatile organic compound (VOC) emissions from livestock operations have been adequately validated for accuracy. Flow-through flux chambers and wind tunnels are sometimes used; however, ammonia and VOC flux from pen or pond surfaces are affected by atmospheric turbulence, atmospheric concentration, and temperature, all of which are altered by a chamber. To determine the effects of air exchange rate on ammonia flux, in two lab studies we compared ammonia flux from an “unaffected” source to the same source when the air exchange rate ranged from 0 to 4 turnovers/minute. Buffered ammonium sulfate solutions (pH = 7.6, 8.6, and 9.6) were used as a surrogate ammonia source to simulate a feedlot retention pond. Similar buffer solutions were added to a cellulose media to simulate a feedlot pen surface. With both simulated surfaces, ammonia flux increased with increasing air turnover rate. Flux at 4 turnovers/minute were approximately 2x flux at 0.5 turnovers/minute and 50% of flux from unaffected containers. In a third lab experiment, VOC flux was measured from fresh cattle feces and retention pond effluent using a wind tunnel with air flow rates ranging from 0.5 to 9.7 meters/second (approximately 1 to 32 turnovers/minute). In general, VOC flux doubled for each 2-fold increase in air flow rate. Previous chamber studies have noted a large spatial variability in ammonia flux from pen and lagoon surfaces with CV ranging from 23 to 192%. Based on 11 chamber studies, the number of ammonia flux estimates required to be 95% confident that the estimated mean is within 20% of the true mean (determined as CV2/100) ranges from 5 to 369; with a mean of approximately 75. These findings suggest that flux chambers will not give accurate estimates of ammonia or VOC flux from pen or lagoon surfaces and that large numbers of samples may be required when using chambers for treatment comparisons.