@stevenroose pro tip, this doesnt have to be liquid nitrogen. If you have access to dry ice (much easier to get) all you would need to do is mix a few chips in with acetone and it would be just as effective. The problem is making sure there are no fumes in the can. You could just pour it over the tear gas maybe to reduce that risk. I would have to experiment to see good ways to prevent fumes being an issue.