I'm pretty sure mist/smoke particle effects just render that way. Which is unfortunate, because Mists/Smoke effects are the key atmospheric effect for this server. Furthermore, those smoke stacks on top of the buildings in the city are part of the tileset, Vallaki uses the base tileset from NWN. You can't actually select the smoke stacks, they're just part of the terrain per-se.. The only way to get around it would be to rebuild Vallaki on either a different tileset (vastly changing its appearance) or somehow developing a modified version of the base nwn tileset that is exactly the same, minus smoke stacks, which is like creating a new 3D Model for it.