Can a negative charge ionize air? Can a negative charge ionize air? Adding to this question, I have studied that positive charge ionizes air but never studied that negative charge ionize air. If possible, please explain how does it ionize air?
 A: Ionization of this sort is not caused by positive or negative charges per say, but by an electric field. We can view the ionization as the electric field trying to accelerate the electrons and nucleus of an atom in opposite directions and ripping them apart.
(In reality, this is a minor effect. Most ionization is caused by a chain reaction as free electrons are accelerated and collide with other molecules, ionizing them).
Therefore to get ionization we need to setup a large electric field. To achieve this generally a positive and negative charge are used. For example in a glow discharge.
I guess if you had a single positive or negative charge in space it could generate a big enough electric field near it to cause ionization. This would be somewhat similar to what happens in lightning.
You can also have ionization due to other sources such as thermal ionization in stars but I don't think that is what is asked about here.
A: Both positive and negative charges can produce ionised air molecules, but the mechanisms are different.
A positive charge attracts electrons produced by background radiation. The high field strength accelerates these electrons and the electrons collide with and ionise air molecules. The electrons from the ionised air molecules are in turn accelerated towards the positive charge and they collide with and ionise more air molecules. The result is an electron avalanche. So the positive charge produces positive ions.
A negative charge produces electrons by field emission. If the charge is high enough it reduces the work function of the electrode to zero and electrons are released from the surface. These electrons then bind to air molecules to produce negative ions, so a negative charge produces negative ions.
Both types of ionisation are examples of corona discharge.
