Pollution
Pollution is represented as an abstract "cloud", calculated per chunk every tick and visible on the minimap and Map, when Alternative view is on (default Alt-Key).
It is produced by many buildings involved in processing items and spreads outwards at a steady rate.
The evolution factor is not increased by the spreading/absorbed pollution, but by the pollution produced by all your machinery at every tick. The pollution cloud is used to trigger biter attacks and determines the size of the attacks.
Pollution spread
As soon as a chunk has reached 15.0 pollution it starts spreading in all four cardinal directions at a rate of 2% per tick.
e.g. a chunk with 400.0 pollution and 4 adjacent chunks with 100.0 pollution each, raises the pollution in all adjacent chunks by 8.0 while reducing its own pollution by 32.0. But everyone of the 4 surrounding spreads 2.0 pollution "back" to the center chunk, so it only loses 24.0 + absorbed value.
Pollution dissipation
- Every Chunk (32x32) of map slowly reduces the pollution it covers (See Pollution Production#Chunks). So the more the pollution spreads, the more is absorbed.
- Trees also absorb some pollution (See Pollution Production#Trees).
- Spawners absorb a great amount of pollution.
- In certain Mods it is possible to build devices or trees which reduce pollution.
Native life
Pollution attracts biters to your factory. Biters who find themselves in a polluted area will attempt to reach the source of pollution and destroy it.
Each spawner absorbs 20 + 0.01 * [chunks pollution] every tick, if the chunks pollution is greater than 20 otherwise it absorbs the total pollution.
Higher pollution values decrease the time it takes for biters to join the attack force. After a certain amount of pollution is absorbed the spawner sends one of its biters/spitters to a rendezvous point. Every 1 to 10 minutes (random) the mustered biters launch an attack. If not all biters have arrived at the rendezvous point by that time, they will wait up to an additional 2 minutes for stragglers.
Required pollution to add an additional biter/spitter to the attack wave:
| Pollution | Type |
|---|---|
| 200 | Small biter |
| 1000 | Medium biter |
| 4000 | Big biter |
| 20000 | Behemoth biter |
| 200 | Small spitter |
| 600 | Medium spitter |
| 1500 | Big apitter |
| 10000 | Behemoth spitter |
With 1350 absorbed pollution at the time of attack the following wave consists of 6 small biters and 1 medium biter OR 6 small spitters and 2 medium spitters depending on the spawner's type and evolution factor.
Modules
Modules that list "+x% pollution" increase pollution multiplier, not a flat pollution rate. Final pollution value is (pollution multiplier * energy usage multiplier * base pollution), meaning heavily boosted buildings are likely to account for most of the pollution produced in a factory.