Lungs clean themselves through coughing. Our lungs have cells that have protruding hair or cilia and goblet cells that produce mucus; the mucus and the hair trap particulate matter and germs. The mucus flows all over the lungs and is expelled or swallowed to eliminate dirt through a cough.
How do lungs clean themselves? – http://wiki.answers.com/Q/How_do_lungs_clean_themselves