## 2 Materials and Methods  
### Digital Rearing Chamber Inspection System  
The digital rearing chamber inspection system is shown in Figure 1. The rearing chamber dimensions were 1.2 m \(\times\) 1.2 m \(\times\) 1.2 m, with the feeding trough and watererer above the chamber. The air inlet and outlet were both 100 mm in diameter, and they were located on the left and right sides of the box. Three air inlets were arranged on the upper left side, and one air outlet was arranged on the lower right side. A 0.8 m L \(\times\) 0.6 m W \(\times\) 0.6 m H iron cage was placed inside. The iron cage was located on a stainless-steel base. An axial fan (SE-A100, Shenzhen, China) was installed at the air outlet for negative pressure ventilation. The broiler's growth parameters were measured by weight sensors. An infrared acoustic-spectrum gas-detection analyzer (INNOVA1412, LumaSense, Ballerup Kommune, Denmark) and a multipoint gas sampling apparatus (INNOVA1409, LumaSense, Ballerup Kommune, Denmark) were used to detect the NH\({}_{3}\) and CO\({}_{2}\) concentrations. The INNOVA analyzer was challenged yearly and calibrated, as needed, with 0 ppm, 25 ppm NH\({}_{3}\) (balanced with air), and 3000 ppm CO\({}_{2}\) (N\({}_{2}\) balance) span calibration gases. The digital rearing chamber was connected to the analyzer sample inlet and outlet with two 3 mm tubes, and sample air was extracted from the digital rearing chamber, circulated through the analyzer sample chamber, and then returned to the digital rearing chamber. The ammonia detection limit of the photoacoustic analyzer was 0.2 ppm, and the sensitivity to water vapor was compensated. Before the start of the test, the gas-sampling instrument was zero-adjusted and calibrated with an S4000 gas dilution calibrator from Envoronics, Tolland, CT, USA, with a sampling interval of 10 min. A filter (diameter: 4.5 cm; 4.5 \(\upmu\)m) was installed in the sampling pipe for gas sampling through a Teflon tube (1/4 inch).  
### Digital Rearing Chamber Inspection System  
Gas determination can be influenced by air flow in the chamber. To avoid dead corners of ventilation, ANSYS was used for simulating the airflow field direction and mode inside the rearing chamber, and then determining the position, size, and number of inlets and outlets. Based on the ventilation rate (10-25 times/h), the rearing chamber volume (1.49 m\({}^{3}\)), and the air speed inside the rearing chamber (less than 1 m/s), a flow field simulation was run; the results are shown in Figure 2. The simulation results showed that when the inlets were on the left and the outlets were on the right, the air inside the chamber was distributed evenly, and the air circulation covered the entire rearing chamber space with no ventilation dead corners in the broiler activity area. This reduced the aggregation of NH\({}_{3}\) and CO\({}_{2}\) in the rearing chamber and ensured normal growth of the broilers. Moreover, check valves were installed at the inlets to prevent NH\({}_{3}\) and CO\({}_{2}\) from escaping.  
Figure 1: Schematic representation of the multirearing environmental chamber system for growth parameters and air emission measurement.  
Figure 2: Airflow field analysis diagram of scheme: (**a**) streamline of air flow field; (**b**) wind speed contour map.