Particles between 0.5µm and 3µm in size are filtered by the nasal mucosa and transported by cilia propulsion to the nasopharynx. Filtration of particulates in the human nose, 1998. N95 masks are designed to be worn for protection in contaminated environments. They are designed and approved to capture 95% of non-oil-based matter greater than 0.3µm. … More On the Nose and Up the Nose