Ammonium Nitrate seems plausible. I am not sure why it was confiscated and from whom...
I think this "halo" means, that the air is driven out above speed of sound. I have seen similar things as I was in the Army with airplanes.
When Ammonium Nitrate explodes you don't see this Halo. It must be another explosive with a higher burning speed.
Have you seen the explosion in the Russian weapons storage? You find it in the first video at 0:20 following. This looks exactly like the explosion in Beirut, but on a smaller scale. The halo is clearly visible.