There is video footage of nearby villages in Pripyat, in the first week after the Chernobyl disaster. When I watch it there are villagers leading normal lives in normal clothing. Some Russian nuclear scientists pass by in full radioactive suits. Then there these clearly visible "flashes" in the air; I have looked on youtube but haven't found the video that I watched a long time ago. My layperson understanding is that these flashes are caused by an extreme amount of radiation.
Here's footage that shows the flashes in the air. They are subtle orangish flashes that are quick. But there's one for instance just after 3 minutes. This isn't the original one that showed the flashes better. Anyway: Chernobyl
From Wikipedia "Ionized-air glow":
Within minutes after the steam explosion that caused the Chernobyl accident at 01:23 local time, a number of employees at the power station went outside to get a clearer view of the extent of the damage. One such survivor, Alexander Yuvchenko, recounts that once he stopped outside and looked up towards the reactor hall he saw a "very beautiful" LASER-like beam of light bluish light, caused by the ionization of air, that appeared to flood up into infinity.
My questions are:
What amount of radioactive material is needed to make those flashes in the air happen?
Is radiation alone enough?
Are other factors such as weather, temperature or other prior chemical elements in the air needed to allow this flashing to happen?