Basically, smoke is composed of two components, gases and particulate solids. The gases leave your lungs when you exhale, while some of the solids remain, and c

Basically, smoke is composed of two components, gases and particulate solids. The gases leave your lungs when you exhale, while some of the solids remain, and cause cancer and other bad things. The concentration of particulate solids is many orders of magnitude greater in tobacco smoke than marijuana smoke, which is why the smell of tobacco smoke will persist in an enclosed space for years, while the smell of marijuana smoke completely dissipates after only a few hours.