Volatile Ammonia Fraction and Flux from Thin Layers of Buffered Ammonium Solution and Dairy Cattle Manure

Abstract

Process-based models are being used to predict ammonia (NH 3) emissions from manure sources, but their accuracy has not been fully evaluated for cattle manure. Laboratory trials were conducted to measure the NH 3 volatile fraction (undissociated NH 3 fraction divided by Henry's law constant) and volatilization flux from buffered ammonium-water solution and dairy cattle manure. Effects of ionic strength, ammoniacal N concentration, temperature and pH of the media, and air velocity over the media were evaluated. As represented in existing models, media type, temperature, and pH were verified to influence the NH 3 volatile fraction and mass transfer. Model prediction underestimated the volatile NH 3 fraction by 5% in solution trials and 94% in manure trials. This underestimation was attributed to an increase in surface pH created through the emission of carbon dioxide (CO 2). Ammonia emission rate from both the ammonium solution and manure surfaces was affected by temperature and air velocity. A frequently used dairy manure volatilization model predicted NH 3 emission rates from manure surfaces more accurately than that from buffered solution with average errors of-16% and +81%, respectively. Temperature significantly affected the difference between predicted and measured rates, with the greatest error at temperatures over 25°C. The results imply that further model development is needed to improve the accuracy of predicting NH 3 emissions from dairy cattle manure with an emphasis on the measurement and prediction of manure surface pH as affected by CO 2 emission.

Spatial and Temporal Variation in Physicochemical Properties of Dairy Lagoons in South-Central Idaho

“…Changes in lagoon water pH can vary with the emissions of both NH 3 and CO 2 . The formation of NH 3 in solution generates H + and reduces the pH, and the formation of CO 2 (utilization of H + ) in solution increases pH (Ni, 1999;Chaoui et al, 2009). It has been demonstrated on dairies in southern Idaho that emissions of both NH 3 and CO 2 occur from lagoons and typically increase from spring to fall following increases in temperature (Bjorneberg et al, 2009, Leytem et al, 2011, 2013.…”

Refining a model-based assessment strategy to estimate the ammonia emission from floors in dairy cow houses

“…Below a pH value of about 6 to 7 there is mainly NH + 4 while above 7 the NH 3 part increases, and above about 11 there is mainly NH 3 (Monteny & Erisman, 1998). The NH 3 emission process, and the related CO 2 emission process, in itself influence the pH level in a urine puddle (Blanes-Vidal et al, 2009;Chaoui et al, 2009;Hafner et al, 2013) and these processes are dynamic. The amount of volatile NH 3 depends on the Henry's law constant, which describes the equilibrium between NH 3 in liquid and gas form.…”

“…In the current mechanistic models, the input variable pH is assumed to be a constant value with a pronounced effect on estimated NH 3 emission (Aarnink & Elzing, 1998;Chaoui et al, 2009;Elzing & Monteny, 1997;. This assumption is questionable, because NH 3 emission is a dynamic process in which the pH is an indicator and not an input variable (Blanes-Vidal et al, 2009;Chaoui et al, 2009;Monteny, 2000;Sommer & Sherlock, 1996).…”

“…This assumption is questionable, because NH 3 emission is a dynamic process in which the pH is an indicator and not an input variable (Blanes-Vidal et al, 2009;Chaoui et al, 2009;Monteny, 2000;Sommer & Sherlock, 1996). According to Blanes-Vidal et al (2009 and Hafner et al (2013), the pH initially increases because acid gas CO 2 is emitted.…”

“…Therefore, he hypothesised that pH values measured inside cow houses may be higher compared to lab experiments. Finally, the mentioned studies (Blunden & Aneja, 2008;Chaoui et al, 2009;Monteny, 2000) were performed with closed jars in a lab. Thus, they did not represent the actual situation in a cow house.…”