How particulate matter is breathed into the human body is dependent on the size of the matter.
Particles smaller than .1 micrometers tend to deposit in the tracheobronchial tree and are removed when exhaling. Particles between .01 and 2 micrometers penetrate deep into the lungs and settle in respiratory bronchioles or alveolar sacs. These particles stay in the lungs. Particles larger than 2 micrometers do not penetrate beyond the nasal cavity or trachea. They exit the body during a cough or sneeze.