I suffer from this too- phantosmia. The doctor said that sometimes people who work outdoors all day cutting grass have this problem due to sinus problems and pressure on a nerve that runs along the back of the skull. It drives me insane. It started out like second hand cigarette smell, lately if I walk onto any place that has a grill like Waffle House or even if I cook burgers on the stove top at home - a funky burnt grease smells gets stuck in my nose .
Oddly, before I didn’t have to be around cigarettes burning to smell them. I don’t smoke- nor have I. It does burn my nose for a few days with the onset. I have to use A Vick’s vapor stick for about a week. Very very annoying!!!