The Trollwinds

Tanneries, slaughter houses, dyers, smelters, and other concerns that produce excessive waste, noise, or stench have long been banned from setting up shop within the city walls unless the propreitor has extremely important connections or is willing to pay exorbitant bribes in order to secure the proper permissions and permits. As a result, most industries of this type have been forced to locate along the Oregvez River flood plain to the east of the city. For reasons that are obvious to anyone who's ever been there, this area has earned the name "Stinktown." 
Most of the time, the prevailing winds carry the stench and some of the noice of Stinktown away from the city, either northeast along the river or to the south across the seas. From time to time, however, the winds will change course and carry the unpleasant aromas of Stinktown through the city. The stench is usually unpleasant but bearable, but in certain conditions (or when encountered by someone wholly unaccostomed to such assaults on the senses) the foul wind coming from stinktown can cause nausea, dizziness, retching, and vomiting. 
Somewhere along the line, the foul winds that sweep into the city from Stinktown were given the name "The Trollwinds." The most explanation of the name's origin involves some long-ago wordsmith obsevering that the winds smelled like what they'd imagine a troll's bunghole to smell like.