Then why we are talking about photons, and not just oscillating electric field? Why light does not have voltage? Interesting debate: https://physics.stackexchange.com/questions/495219/can-air-be-ionized-using-microwaves
Yes, you can achieve air discharge in the atmosphere using high power microwave radiation. The mechanism is avalanche ionization (https://apps.dtic.mil/dtic/tr/fulltext/u2/a172227.pdf)
Just to be clear, the breakdown (ionization) of air, or any insulating material for that matter, is a voltage phenomenon. That voltage can be at any frequency, including microwave frequency. But if it not the electromagnetic energy (photon) of the microwaves that is causing the breakdown, but the magnitude of voltage. – Bob D Aug 4 '19 at 19:58
@BobD : I have not heard about electromagnetic radiation without voltage. If it is not electromagnetic energy of the microwaves that causes the breakdown, what is the source of the energy required for breakdown? (I hope it is obvious that air has higher energy after breakdown.) If your reasoning were correct, it would have been applicable to laser radiation as well, as visible light cannot cause one-photon ionization of air. –
Microwaves can cause hydrogen dissociation from my first hand experience so the argument that a single microwave photon does not have enough energy is not convincing. – my2cts Aug 4 '19 at 20:42