I don't really understand the mechanism of electrical breakdown, as occurs in a spark gap.
I know that once a certain voltage threshold is passed (around 30kV/cm in air) a gap in a circuit can become electrically conductive, drastically reducing the resistance of a gap and producing a spark while the current flows over the gap.
Usually it's explained like this: The strong electric field across the gap ionizes the air, which now becomes conductive. But could somebody explain it to me in more detail? I mean, the air ionizes, but what does it mean? Are the molecules somehow arranging themselves so that different charges "point" different ways? Or are the "electrodes" of the gap somehow attracting different kinds of particles from the air? Or are the air molecules losing electrons? And how does any of this make the electrons from the high voltage side cross the gap to the lower voltage side? Thank you!