First off, I hope this question is not too offensive. Discussing technicalities of a genocide will certainly disgust some. I am in no way trying to condone nazi crimes. I am also not sure whether it makes sense to search for rational thought in genocide. Here goes anyway:
Nazi death camps used shower heads to introduce a gas into the gas chambers, thereby killing people. The gas used was Zyklon-B, an industrial product produced by a single supplier, and likely relatively expensive. It also meant that the gas chambers had to be aerated for a number of minutes before soldiers or forced laborers could enter the gas chambers to drag out the corpses.
Why didn’t they simply use CO2? It’s a byproduct of basically any fire. It’s cheap and could have been produced on-site trivially. It’s also part of normal air and only toxic in high concentrations, likely meaning less danger to soldiers.
I think that’s carbon monoxide. CO
CO kills by sending you to sleep and then binding to oxygen very tightly in the blood asphyxiating you.
CO2 drives the breathing cycle and causes you to unctrollably hyperventilate. You tend to die of a heart attack through panic.
Very different. I suspect a large crowd of people panicking would be very difficult to control.
I think you gave another reason yourself. Smaller quantities of toxin are easier to manage / use.