You should do a late game tech called "Air scrubber" or something similar that reduces the pollution inside the building. Maybe 20-40%?

Edit- I just saw that this is planned but Air scrubber is an actual name of a pollution reducing machine in real life. It typically uses water to pull the pollution out of the air and then the pollution is dealt with in another manner. Typically via a local water treatment plant.

In the meantime, check out the Air Filtering mod if you haven't already. Not quite as convenient as the factory simply reducing pollution, but pollution reduction is quite strong in its own right.