After rebalance in mod version 1.0.4 pollution cloud doesn't trigger strong biters attacks from neighbouring nests. Looks like only touched nest sends attack squads. But those squads are small and too rarely sent (probably smaller than vanilla generates even without deathworld setting). Previously it were more global attacks almost equal to revenge for raiding enemy nests. The difference is especially notable if biters bases are settled with enough density.
In other words pollution now doesn't provoke special very aggressive attacks like it was in all previous Rampant mod versions, but only generates additional "anger" for usual actions - attacks, nests expansion, ...
As a consequence there is no need now for player to work with pollition: to use air filters, to keep forests, to position pollution producing buildings away from enemies and so on. There is no need to destroy nests in pollution cloud zone unless those nests are too close to turrets to trigger real revenge with death of attacking biters near them.
