Hmm, I think you are shooting a bit too far.

A quick estimate says that to generate ~1MeV gamma rays required for the electron-positron pair production you need at least 1MV potential difference between the towers, or >10MV/m electric field, given that the distance between them is < 100m. The dielectric breakdown strength of air is about 3MV/m, so you are not even at 30% of the minimum required energy, not accounting for any losses.

Maybe they can somehow build up enough voltage by isolating the electrodes with paraffin, Teflon or even glass, then extremely quickly open a gap for the discharge to take place, but this is quite hard to do and their current design implies nothing like that.

According to the comments, they are much more likely to play with the Schumann resonances, which is a rather more modest objective.