Chimney odors are annoying problems, and there can be one or more factors contributing to your chimney odor issue.
Here in Maryland we are very familiar with humidity during the summer months. The moisture from the humidity interacts with the soot creating the pungent camp fire smell. In addition, if the chimney is allowing water to enter the masonry structure this increased moisture will intensify the smell.
Secondly, animals that nest in your chimney can leave behind nesting material and droppings. The longer the animal keeps residence in your chimney the odor will most likely get worse. Unfortunately, sometimes one or more of the animals may expire in the chimney which can cause odor.
Another culprit is a dirty flue. Build up of ash and soot from use throughout the season and or not having your chimney cleaned on a regular basis resulting in years of build up of soot and creosote.
Finally, air pressure can play a role in chimney odors. The normal way that air flow should move through a chimney is up. However, this can be reversed by the use of furnace air handlers and exhaust vents for your kitchen and bathrooms. The air from the outside can be drawn down the chimney into the room when the air conditioner turns on or you use your exhaust vent.
As you can see there are several factors that can cause your chimney odor problem. Call your certified chimney professional to inspect and determine what may be the cause of your chimney odors.