The idea is this, form stage 2 of structures, that factory buildings should have a vent spot form outside, the pollution would be vent form the spot, unless the spot were connect to a filter system to filter the pollution out (like how pump works, but for pulling pollution out form structure to sent them away through special pipes into filter buildings to get rid the pollution for slowing down the swarm detect your base, or lure them into well defensed spots to avoid them rampage through your base.), the spot would sent out all pollution form inside the building.
Also suggesting if possible, make a inside plugin to filter pollution form air into liquid pollution and need to send them to burn somewhere else, so your main base would be pollution free/low.