Air vents accelerate biter evolution.

[YurgenJurgensen]

Because air vents absorb and reemit pollution, passive air vents generate and consume hundreds of thousands of pollution per hour, which causes the evolution factor to rapidly increase, making combat more difficult than intended.

[NathaU]

Ah you mean that pollution which already continued to the evolution factor, does the same again when moved through a vent? I'll look for a way to prevent that. Hoped that polluting with a negative number also affects the factor in a positive way YurgenJurgensen ***@***.***> schrieb am Di., 29. Juli 2025, 20:06:

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*YurgenJurgensen* created an issue (NathaU/factorio-subsurface#39) <#39> Because air vents absorb and reemit pollution, passive air vents generate and consume hundreds of thousands of pollution per hour, which causes the evolution factor to rapidly increase, making combat more difficult than intended. — Reply to this email directly, view it on GitHub <#39>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ARG36MYI7PG23N6ISKF6FGL3K6Z2ZAVCNFSM6AAAAACCUVTIHCVHI2DSMVQWIX3LMV43ASLTON2WKOZTGI3TINJRHE2DEMQ> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[YurgenJurgensen]

Something like that. I think it’s more than double-counting. Everything else in the factory had created less than a million pollution, but the passive air vents were at over fifteen million total. I think the passive air vents move a lot of pollution back and forth over and over again, and it counts for evolution every time.

[NathaU]

The evolution factor is surface-based, so in generel this shouldnt be a problem (of course polluting with a negative amount does not decrease the factor).

Normally factories have a constant pollution over time, so the passive air vents move pollution only in one direction. Is this different for you, do the pollution gradients change over time a lot (which would cause the vent to switch between downward and upward moving)

[YurgenJurgensen]

I had a pollution combinator set up to switch off power to the underground mines if pollution got too high, so it could result in the flow reversing quite a lot. Or, I had multiple air vents in adjacent chunks, so it’s possible that a loop formed where one let pollution flow up and one flow down. They’ve all been replaced with active vents now anyway, which don’t seem to have that problem.