These are nothing more than wide places in the exhaust flue where larger particles can settle out of the exhaust gas stream.
仅仅是排气通道中的一些宽阔区域，较大的微粒会在其中沉积，这样排出的气体中就只有较小微粒了。
2
The control of gases involves the removal of the pollutant from the exhaust gas stream, a chemical change in the pollutant, or a change in the process producing the pollutant.