|Cole, Noel - Andy|
Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/1/2005
Publication Date: 7/20/2005
Citation: Rhoades, M.B., Parker, D.B., Auvermann, B., Cole, N.A., Perschbacher-Buser, Z., Deotte, R.E. 2005. Factors affecting emission measurements with surface isolation flux chambers. In: American Society of Agricultural Engineers Annual International Meeting Technical Papers, July 17-20, 2005, Tampa, Florida. Paper Number 054026. 2005 CDROM. Interpretive Summary: There is increasing concern among agricultural producers, regulators, and the general public about the effects of agriculture on air quality. Among the potential pollutants of most concern are odors, dust, and ammonia. Unfortunately, it is very difficult and expensive to measure emissions of these pollutants; therefore, little information is available concerning emissions of these pollutants from agriculture. Livestock feeding operations are considered to be a major source of ammonia emissions. In the past, some scientists have used different types of flux chambers to estimate emissions. However, many of these chambers have not been adequately tested to determine the validity of values obtained using them. This experiment was conducted to evaluate the effects of several factors on estimated ammonia emissions from the surface of a feedlot or dairy. Three types/sizes of chambers were compared for North Carolina State, EPA, and West Texas A&M. The volume of air pulled through the chambers was varied from about 0.1 to > 1.0 turnovers per minute. Chambers were placed on areas that should have low ammonia emissions (dry areas without fresh feces or urine) and areas that should have high ammonia emissions. With low emissions, air flow rate did not affect calculated emissions, however, with higher emissions the calculated emission rate was directly proportional to the air flow rate through the chamber. Variations in emissions in locations within a pen were very large. These studies demonstrate that use of flux chambers are valid for treatment comparisons but emission rate measured using flux chambers will potentially greatly underestimate true emission rates because of effects on the microclimate within the chamber.
Technical Abstract: We conducted field experiments to evaluate how factors such as sweep air flow rate, time since urine deposition, and flux chamber footprint area affect ammonia fluxes from open-lot feedyard and dairy surfaces as measured using three different flux chamber designs. The chambers included a 26.5-cm diameter chamber (North Carolina State University design), a 49-cm diameter chamber (EPA-type design), and a 1.2 m x 2.4 m rectangular chamber (West Texas A&M University design). Clean sweep air collected upwind of the feedyard (<50 ppb NH3-N) was supplied to the chambers using a large compressed air tank, and ammonia concentrations were measured using a Thermo Environmental Instruments 17C chemiluminescence NH3 analyzer. Ammonia fluxes increased up to 10-fold between sweep airflow rates of 0.1 and 1.0 volumetric changes per minute. Ammonia fluxes from urine spots were highly dependent on the time since the urine was excreted. In one instance, the flux decreased at 57 ug/m2/min for every minute elapsed during the first two hours after excretion. Maximum fluxes and variability among individual flux measurements decreased with increasing flux chamber footprint area. A better knowledge of how these factors affect calculated emission rates will be beneficial to future development of emission factors for open-lot feedyards and dairies.