How does an ionizer emit ions into the air?

I understand the process of common houshold air filters using an ionizer to emit ions into a room to bond with particles in the air causing them to fall and no longer be in the air. But what mechanism (mechanial, elctromagnetic, etc.) is used to propell the ions into the room. Are different sizes of the device used for different sized rooms? Any other info would be interesting.
I understand the process of common houshold air filters using an ionizer to emit ions into a room to bond with particles in the air causing them to fall and no longer be in the air. But what mechanism (mechanial, elctromagnetic, etc.) is used to propell the ions into the room. Are different sizes of the device used for different sized rooms? Any other info would be interesting.
Thanks for the response. I'm not looking to remove any odors. I just use an room air filter that has an ionizer that doesn't require the fan to be in operation for it to work. It made me wonder how does an ionizer emit ions then.