## 3 Results and Discussion
### Diurnal Concentration and Emission Profiles  
#### 3.2.1 CC and AV  
The diurnal patterns of average VR, NH\({}_{3}\) concentrations, and emissions in CC and AV, were plotted in Figure 3. The VR ranged from 1.21 to 5.15 m\({}^{3}\)/h-hen for CC, and 0.84 to 12.16 m\({}^{3}\)/h-hen for AV. In CC and AV, VR presented a variation pattern following that of outdoor temperature, which showed a peak within 9:00 to 20:00 in both days of a complete manure removal cycle, because of the high temperature, and it did not change greatly at the time of manure removal (11:00-12:00, and 16:00-17:00). Figure 3(a2,b2) depicted the temporal variations in NH\({}_{3}\) concentrations during manure removal (day 1) and the day after manure removal (day 2). On both days, concentrations of NH\({}_{3}\) in CC were higher during the night, due to cooler temperature and lower VR, which has been supported by many studies with the same production system [12; 18; 26]. NH\({}_{3}\) concentrations in the CC ranged from 0.63 to 3.79 mg/m\({}^{3}\) (2.01 \(\pm\) 0.93 mg/m\({}^{3}\) in average), which were comparable with the average  
Figure 3: Diurnal patterns average VR, NH\({}_{3}\) concentration, and emissions in CC (**a**) and AV (**b**). (Day 1 means the day with manure removal; Day 2 means the day after manure removal. Error bar was plotted by using standard deviation. )NH\({}_{3}\) concentration in similar facilities with the ambient temperature over 25 \({}^{\circ}\)C and stock density of 516 cm\({}^{2}\)/hen in the US midwest (near to 38\({}^{\circ}\) N) [27; 28]. It could be seen that NH\({}_{3}\) concentrations kept stable on the second day after manure removal in AV. Before 10:00, the VR increased gradually as the indoor temperature increasing to emit the NH\({}_{3}\) out of the house to keep a stable indoor NH\({}_{3}\) concentration. The phenomenon occurred again after 20:00. As known, the hens were more active comparatively during the daytime, while, the indoor temperature, VR, and NH\({}_{3}\) concentration in AV remained fairly constant during 12:00-20:00 on the second day, which illustrated that animal activity did not have a significant effect on NH\({}_{3}\) concentration after separating the manure from hens kept inside the avary units since the manure was the main NH\({}_{3}\) source [28; 29]. NH\({}_{3}\) concentrations in AV ranged from 0.54 to 1.30 mg/m\({}^{3}\) (0.77 \(\pm\) 0.19 mg/m\({}^{3}\) in average), which were significantly lower than that in summer (about 2.12 mg/m\({}^{3}\)) in a similar type of house with lower VR (maximal VR of 0.75 m\({}^{3}\)/h-hen) and longer manure accumulation (3 to 4 days) inside the operation that [PERSON] et al. [27] studied. On the day after manure removal in CC and AV, NH\({}_{3}\) emission rates were higher in the daytime and lower in the nighttime, which agreed with [PERSON] et al. [16] and [PERSON] et al. [30]. It was likely influenced by the house temperature and VR. High temperatures can accelerate microbiological degradation of manure to promote bigger generation rates of NH\({}_{3}\)[16]. [PERSON] et al. [14] also observed that VR had a significant effect on NH\({}_{3}\) emissions and caused higher emission rates during the daytime. After manure removal, NH\({}_{3}\) emission rates in both houses sharply dropped down. The NH\({}_{3}\) emission rates within a whole manure removal cycle ranged from 0.92 to 6.52 mg/h-hen (3.43 \(\pm\) 1.46 mg/h-hen in average) in CC, which was comparable with reported values of 4.04 and 2.83 mg/h-hen in laying hen houses with CC and similar management in the U.S. Midwest [27] and 3.60 mg/h-hen for a traditional cage with manure belt-natural drying system with a 492 cm\({}^{2}\)/hen stocking density in the laboratory [31].