So essentially, when we breathe in we can either breathe in through our mouth, or we normally breathe in through our nose. Now, when we breathe in through our nose, the air, and this includes things like nitrogen oxygen that moves in to our nasal cavity, the nasal cavity, or the canals found within our nose. Now, the lining of the nasal cavity consists of a special type of slimy and sticky membrane known as the mucous membrane. And the mucus membrane is secreted and created by specialized cells known as goblet cells. Now, as the air travels through our nasal cavity, the pollutants and bacterial cells and other harmful substances essentially get stuck within this mucus membrane. So we see that the nasal cavity, because it contains these tiny extensions known as cilia, as well as a mucus membrane that helps trap this harmful substance, the nasal cavity actually functions in the process of filtering.