a small aquarium air pump which is placed on the outside on the cage with a piece of tubing, often called air line placed into the cage is a good way of providing a supply of fresh air.
Points to watch are ;-
A cold draft being created if the air being pumped in is too cold or too fast.
Pollution from smoke, air freshers etc, etc
unlikely, but make sure the ants cant crawl up the air line, possibly place an air stone/brick on the end.
DON'T TAP THE GLASS PLEASE