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Air as a conductor You read that air is an insulator.For a spark or lightning to occur, freely moving charged particles must be formed in air, which is normally neutral.The spark that jumps between your finger and a doorknob after you have rubbed your feet on a carpet discharges you.In the case of lightning, excess charges in the cloud and on the ground exert enough force to temporarily remove electrons from the molecules in the air.

Air as a conductor You read that air is an insulator. Under certain conditions, charges can move through air as if it were a conductor. The spark that jumps between your finger and a doorknob after you have rubbed your feet on a carpet discharges you. In other words, you have become neutral because the excess charges have left your body. Similarly, lightning that you see in a thunderstorm discharges a thundercloud. In both of these cases, air becomes a conductor for a brief moment.
When does air become a conductor? To answer this question, recall that electrons are free to move in conductors. For a spark or lightning to occur, freely moving charged particles must be formed in air, which is normally neutral. In the case of lightning, excess charges in the cloud and on the ground exert enough force to temporarily remove electrons from the molecules in the air. The electrons and positively charged ions form a plasma, which is a conductor.