I do a similar thing in my base, at the middle right I have an exit to my base with the same set-up, since its only Co2 there though I do not lose any oxygen unless there is a lot of traffic there. Any excess Co2 drops into my Farming Pit.
This is an old trick I originally used in the morbid oxygen build but since then how doors work have changed a few times. Now they destroy gases again if there is nowhere for the gas to go. So how can we exploit that. Well, simple, CO2 always goes to the bottom right corner of your base, so if you put something there that dupes have to go get, like for example a lavatory that they have to visit at least once per cycle, and you put doors if front of that all CO2 in the base will be destroyed. You can also use it with outhouses and compost heap since we know from tests that polluted oxygen in an oxygen environment does not move up or down but only moves sideways, we can put an outhouse and compost heap behind the doors and all polluted oxygen generated by these will also be destroyed.
Here a quick mash up on how it's built. Note the tiles above the doors are needed to ensure gas in the two middle doors have nowhere to go. It is also best to have an open structure so gases can enter from each side but if you have a small amount of dupes you might want to avoid that as that could also delete a fair amount of perfectly good clean oxygen.