4xfordbronc

Whats great about our lungs is that is has its own defense mechanism. Usually particles >10u (microns) deposit in the nasopharynx (the area in the back of your throat behind the nasal cavities). Due to its larger size the particles make a beeline and moves in a straightline. This is the junk that will be coughed up or sneezed out. It does not necessarily damage your lungs. At 5-10u it can reach the trachea which is your wind pipe. Its when the particulate size gets to <2-5u. When it gets to less than 2u, it can reach the respiratory bronchioles and <0.2u gets to the alveoli, this is where O2 and CO2 are exchanged.

Particles are moved by the mucous and cilia in the bronchioles, this is the part where smoking makes the problem worse. It paralyzes the cilia so you can't get the junk to the surface to cough up. Just a little info.