No.2: Negative ions do not work because they are cancelled out by the same amount of positive ions.

It is thought that the same amount of negative and positive ions exist in the air as a whole. However, more negative ions exist in a small space because they are not all cancelled out. This is why negative ions work.

Technically, an actual product ionizes a particular space only while properly handling positively charged electricity or positive ions which are generated along with their negative counterparts. This is how the product purifies the particular space only in order to supply negative ions to the human body.