# How does a negative ion generator work?

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.

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