The figure illustrates the deposition pattern of particles in the airways as a function of particle diameter. Pollen are larger than 10 µm, mostly between 20-50 µm. How far do they penetrate into the airways, where in the airway do they impact?
That really was an easy question. Obviously such particles will impact at the level of the nose and the pharynx. However, let us take the opportunity to demonstrate the wonderful performance of the upper airways as an air conditioner, protecting the lower airways from exposure to very large particles, which would bring a very large mass of potentially harmful substance to the lung airways. Bear in mind that some substances are hygroscopic, so that in the nasopharynx they may swell from an initially small to a large radius. Therefore, small hygroscopic particles may swell in the nasal airway and not reach the lower airways. Mouth breathers (e.g. during heavy exercise), bypass the nose and hence do not have the benefit of the nasal airway conditioning the air prior to entering the lower airways. Thus the inhaled gas is less sufficiently cleared of particles, as well as cooler and drier.