## 3 Results and Discussion
### Ammonia Emission Rate  
An experiment was undertaken during a 5 h period between 12:30 and 17:30 on Saturday 11 July 2020, in which the high-volume ventilation/scrubber system was turned off in order to measure the flux of NH\({}_{3}\) from the composting manure (Figure 12). Prior to the experiment, under ventilated conditions, internal NH\({}_{3}\) concentrations were stable at approximately 100 mg m\({}^{-3}\), rising to around 150 mg m\({}^{-3}\) as all entrances and exits to the facility were closed. After the ventilation system was disabled, NH\({}_{3}\) concentrations were recorded to drop to an average of ~30 mg m\({}^{-3}\) initially, before rising quickly to reach values of ~250 mg m\({}^{-3}\) within 30 min. Peak concentrations of ~325 mg m\({}^{-3}\) were reached after approximately 40 min. Concentrations of SO\({}_{2}\) followed a similar pattern to NH\({}_{3}\), initially dropping before exceeding the monitoring instrument's detection limit at 1.31 mg m\({}^{-3}\) (500 ppb). It is not clear why NH\({}_{3}\) concentrations dropped after the ventilation system was disabled, but we hypothesize that the negative pressure environment created by the ventilation system caused a greater flux of NH\({}_{3}\) from the manure surface due to the pressure gradient, and therefore, when the ventilation system was disabled, NH\({}_{3}\) was emitted at a reduced rate. Alternatively, the decrease could have been related to lower air turbulence across the manure surface, which would be expected to reduce convective mass transfer of NH\({}_{3}\) from the manure surface to the air [12]. The emission rate of NH\({}_{3}\) was calculated according to Equation (1), based on the time taken for NH\({}_{3}\) concentrations to rise from their minima at ~30 mg m\({}^{-3}\) to the inflection point at ~250 mg m\({}^{-3}\), after which the concentration increase slowed down. The results showed that under stable non-ventilated conditions, the NH\({}_{3}\) emission rate inside the manure agitation hall was between 6.16 and 8.02 (mean = 7.28 \(\pm\) 0.41) NH\({}_{3}\)-N mg min\({}^{-1}\) m\({}^{-3}\) (Table 4); extrapolated, the total mass of NH\({}_{3}\) emitted daily was between 20.7 and 26.96 (mean = 24.47 \(\pm\) 1.39) NH\({}_{3}\)-N kg d\({}^{-1}\). There is little standardization of the units used to report NH\({}_{3}\) emission rates across various studies. The data from this study were compared with other studies in the units in which those studies published their data. The scaled NH\({}_{3}\) emission rates in the PMCF were high compared with studies investigating emissions from AFOs. [PERSON] [12] presented a compilation of data from multiple dairy farms and beef feed lots (\(n\) = 29), where all but one study found NH\({}_{3}\) emissions between 0.01 and 0.9 g h\({}^{-1}\) m\({}^{-2}\), compared with 2.77 \(\pm\) 0.41 g h\({}^{-1}\) m\({}^{-2}\) NH\({}_{3}\)-N in this study. Daily NH\({}_{3}\) emissions from a composting  
Figure 12: Emission flux response to turning off the high-volume ventilation and scrubber system during a 5 h period, 12:30–17:30 on Saturday 11 July 2020.  
facility at a manure belt poultry house were estimated to be much greater, at 596 kg d\({}^{-1}\)[7], approximately 20 times higher than in this study. However, [PERSON] [7] also relayed data from conference proceedings presented by [PERSON] [38], reporting NH\({}_{3}\) emissions of 0.32-2.84 g kg\({}^{-1}\), 0.02-2.74 g kg\({}^{-1}\), and 0.04-0.46 g kg\({}^{-1}\) for composting of swine, poultry, and dairy manure, respectively. These figures are comparable to the NH\({}_{3}\) emissions of 1.52 \(\pm\) 0.09 g kg\({}^{-1}\) from the mixed manure at the PMCF. A separate study of cattle manure composing reported NH\({}_{3}\) emissions of 0.07-0.19 g d\({}^{-1}\) kg\({}^{-1}\) during the first 50 days [39], again similar to the figure of 0.084 \(\pm\) 0.005 g d\({}^{-1}\) kg\({}^{-1}\) for this study. As expected, the NH\({}_{3}\) emission rate at the PMCF was more similar to measurements from other manure composing operations than those from AFOs.