Does pollution ever stop spreading?

[Plawerth]

This is a 0.15.x Marathon 10x cost game. It's getting quite large and slow, and has to run at 50% game speed for anyone to even be able to log on and catch up.

I had this idea that maybe if I killed off all the biters, the game would be less laggy. But as I push the biters back, the pollution cloud seems to get bigger and bigger without limit. I've now put some 12 hours into killing off biters, but the pollution keeps on growing.

When I started the biter clearing, the pollution all fit within the boundaries of the known world, but now the pollution hangs over the edge, and I have to grow the map (already 70+ megabytes) to reach biters that don't want to attack.

Is it just futile to hope the pollution will stabilize and I can get biters to stop spawning and trying to attack the base?

[Koub]

The pollution spreads and is absorbed by :
- the water
- the soil
- the trees
- the spawners

If you push back the aliens far enough so that all the pollution you produce is absorbed by the soil, trees and water, then you'll get out of notice from the biters.

[Edit] : it's very well explained here : https://wiki.factorio.com/Pollution