Minus ion

Today I was talking with my coleague about some electrics. Some years ago, there are many electrics with mechnism to make "minus ion". But I suggest that there cannot appear minus ion in the air of usual condition, 20 degree, 1 atm.

Then I realized that I can't explain the reason for why there cannot exist the minus ion enoughly. I know the reason ambiguously, but I don't know the basic knowledge.

Actually, chemistry was one of the subjects that I dislike. Even that, there are some information in my memory about that.

This time, I was stimulated and want to know more about the mechanism of ion. This night I'd like to look up about that.

What is "ion"?