Each and every industrial building (with the exception of Forest) have a has pollution zone around itself. The size is different for each building and you can see it in the info window.

You can also see it in the city overlay as rusty brown zone around industrial buildings. Train platforms also have 1 square pollution zone around themselves, too. The station buildings and decorations do not have pollution zone, neither do the road stations. It is advisable to block the pollution zone at the train station by placing station upgrades and/or decorations around the platforms.

The Pollution zone '''prevents houses from being upgraded'''. The effect of the pollution zone '''is permanent''' and cannot be canceled by building other city upgrades nearby. You can either have small level 1 houses around industrial buildings as "workers quarters" or you have to place the Construction prohibited extension, or other some other extensions, just to block the area.