## 2 Materials and Methods
### Sampling and Measurement Methods  
Gas concentrations, temperature, and RH were continuously measured in and out of CC, AV, and NM houses from 20 September 2019 to 24 September 2019, 7 June 2020 to 12 June 2020, and 10 July 2019 to 31 July 2019, respectively. NH\({}_{3}\) concentration was monitored by using a portable monitoring unit (PMU) configured with an NH\({}_{3}\) sensor (ME3-NH\({}_{3}\), with a measurement range of 0-50 ppm; Winsen, China, every 20 min. CO\({}_{2}\) concentration was detected in the AV at an interval of 20 min, with a CO\({}_{2}\) sensor (MH-Z14, with a measurement range of 0-5000 ppm, accuracy \(\pm\)100 ppm; Winsen, China) installed in the PMU. Two PMUs were set in CC and NM at the height of 1.5 m, which were fixed close to the air inlet and central exhaust fan. In the AV, three PMUs were located at a height of 1.5 m, were close to the air inlet and cage walls of two aviary cages near the exhaust fans. Temperature and RH were measured by T/RH data loggers (U23-001, HOBO, Bourne, USA), with a measurement ranges of \(-\)40 \({}^{\circ}\)C to 70 \({}^{\circ}\)C and 0-100%, and accuracies of \(\pm\)0.18 \({}^{\circ}\)C and \(\pm\)2.5%, respectively. Three T/RH data loggers were located in the center of the three houses at the height of 1.5 m, and another three loggers were set outside, which were 2.0 m away from the head of laying hen houses. Temperature and RH were continuously monitored by the data loggers.  
Before the experiment, the air velocity of each fan for CC and NM was measured by a hot-wire anemometer (model KA41 L, Kanomax, Osaka, Japan). When measuring, the fan was divided into 4 equal parts by cross-marking, and 2 of them were tested randomly. Each part was evenly distributed with 16 sampling points (Figure 1). The probe of an anemometer was attached to the protective net in front of the fan to measure the air velocity of every sampling point. When the air velocity at a sampling point was comparatively stable, 20 values were recorded continuously by an anemometer, and the average of all sampling velocities was used as the average air velocity through the fan.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Items** & **CC** & **AV** & **NM** \\ \hline Location & 115.06\({}^{\circ}\) E, 36.33\({}^{\circ}\) N & 116.11\({}^{\circ}\) E, 40.08\({}^{\circ}\) N & 113.49\({}^{\circ}\) E, 36.41\({}^{\circ}\) N \\ Elevation/m & 39 & 50 & 583 \\ Breed & Hy-Line brown & Jingfen NO. 6 & Hy-Line gray \\ Animal capacity & 100,000 & 2,952 & 25,000 \\ Cage size/m (L \(\times\) W \(\times\) H) & \(0.6\times 0.6\times 0.5\) & \(4.8\times 2.8\times 3.3\) & \(4.8\times 1.2\times 0.7\) \\ Stocking density/cm\({}^{2}\)/hen & 472 & 711 & 700 \\ Layout & 5 rows, 8 tiers & 2 rows & 4 rows, 4 tiers \\ House size/m (L \(\times\) W \(\times\) H) & \(109.0\times 14.0\times 6.5\) & \(90.0\times 12.0\times 3.5\) & \(120.0\times 12.0\times 5.8\) \\ Ventilation & Mechanical, 6 side-wall & Mechanical, 3 end-wall & Mechanical, 16 end-wall \\ fans, 36 end-wall fans & fans & fans \\  & Every 2 days by manure & Every 2 days by manure & Every 7 days by manure \\ Manure removal & belt, 11:00–12:00 & belt, 16:00–17:00 & belt, 9:00–10:00 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Description of the three laying hen houses studied.