Most humans spend 90% of their time indoors, this is why indoor air quality nowadays is most important topic.
Polluted air has a changed composition, due to smoke, soot, dust, aerosols, fumes and odorous substances. All these additional air particles are breathed in by us daily.
Our natural filters are the mucous membranes in our noses and throats. They can take up particles up to a size of 5 micro metres and therefore protect our lungs from the inhaled particles. Pollen, for example, has a size of 10-100 micro metres. But unfortunately many of the particles in the air are much smaller than 5 micro metres.