Armdriver. Sometimes you may have seen smoke from a chimney falling or even rising & then forming a layer. that is typical of an inversion layer. I have seen where a vent pipe terminates & the smell just permeates the air in a still area outside the house, mainly on cold days, all you can do is extend or relocate the termination of the vent to a more exposed area of the roof. Ask a pilot how inversion works. Maybe Silvan can be of help.