How does a negative ion generator work?

[gabee]

Like this one:

http://www.goldmine-elec-products.com/prodinfo.asp?number=G9695

I understand that it uses some sort of "needle assembly," and electric fields are stronger at sharp points in a conductor and then will ionize the surrounding air at a certain potential. But how exactly are the negative charges isolated in the first place? Some friends and I have discussed how this might happen, such as first charging a capacitor, then attaching the negative lead to such a needle assembly, then grounding the positive lead, but we're not exactly sure.

 

[Mentz114]

I believe the ionisation is caused when an electron binds loosely with a gas molecule. If you put a high -ve voltage on a needle, electrons can escape from the point.

Some friends and I have discussed how this might happen, such as first charging a capacitor, then attaching the negative lead to such a needle assembly, then grounding the positive lead, but we're not exactly sure.

That's about right. The voltage can come from any source, with the +ve grounded.