From "How things work - The Physics of Everyday Life", Louis A. Bloomfield, University of Virginia, USA:
"Household ion generators also remove dust and smoke from room air. These machines resemble electrostatic precipitators but have no internal collecting plates. While they still use corona discharges to charge passing dust grains, they don't attempt to remove the dust from the air. Instead, they let those electrically charged particles, or ions, drift around the room on their own.
"The ions don't drift long because they're attracted to neutral surfaces. A neutral surface contains countless electric charges, and a charged dust grain will attract the surface's opposite charges while repelling its like charges. Because of the forces, the surface's positive and negative charges shift slightly in opposite directions, and the surface becomes electrically polarized. A polarized object is neutral overall but has a positively charged end and a negatively charged end.
"The dust grain and the surface it polarizes attract one another and stick. You can see this effect by charging a toy balloon in your hair and then touching it to a wall. The balloon's charge will polarize the wall, and the two will cling to one another. Thus an ion generator removes particles from the air by sticking them to surfaces in the room. This method is cheap and effective, but the dust ends up decorating the walls and furniture, a problem unless you're fond of the color gray."
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