According to MedicineNet.com, the nasal passage is the channel for nose airflow, carrying most of the air inhaled. The nasal passage is responsible for ridding any harmful pollutants inhaled from the air. The nasal passages also contain the olfactory membranes that provide information regarding airflow to other sensory organs.
About.com states that the nasal passages provide the first barrier to any pollutants that could cause infection in the body. The mucus in nasal passages first traps the irritants, and the hair-shaped cilia pushes the dust, mites, smoke and other pollutants out of the body or through the body towards the stomach acids.