Lightning produces potential differences of many million volts. When an electron or proton goes across the difference of potentials of 1 million volts, it acquires energy of 1 million electron volts, which is enough to produce some high energy x-rays, and even nuclear reactions. Air pressure has an effect though, as the electron won't gain much energy if it keeps colliding with air - unless the electric field strength (volts per meter - it is similar to slope) is pretty high. Lightnings propagate weird -with a streamer going ahead - near the streamer it is plausible that electric field is strong enough.

It's not that different from early linear particle accelerators powered with a big Van-de-Graaf generator. A lot of energy ends up in single charged particle because that particle moved across big potential difference.