Electricity. Air ions are positively or negatively charged air atoms or air molecules. The number and charge depend on the weather conditions. Air ions are produced permanently and neutralized by combination with ions of opposite polarity so that their concentration in the atmosphere varies little.
Air ions can be produced by electric fields in the vicinity of power lines. They can be blown away from the power lines by the wind. The air ions can attach to microscopic airborne particles (e.g., dust). Air ions that are produced by corona discharge at power lines are called corona ions.