Depicted - a liquid oxygen tank vents, and the supercold gas produced hugs the ground. You can see it because it is making the moisture in the air condense. I hope no-one was having a smoke break during this; they would have gone thru their cigarettes fast.
You could do something like what you propose with a temperature differential - an open to the sky park in an alien environment. If you had your park walk sunken down, like a canal, you could flood it with cold oxygen and it would stay down there to some degree, rolling under and pushing up the hotter CO2. O2 is a lighter molecule than CO2 but cold gas is denser that hot gas. You could use that to produce your effect.
Truly you might want to use a cold mix of oxygen and nitrogen in case anyone wanted to smoke in the park.