alt=man sneezing, with<unk> s dispersing widely into the surrounding air A<unk>  is a small aqueous<unk>  produced by exhalation, consisting of saliva or mucus and other matter derived from<unk>  tract surfaces.<unk> s are produced naturally as a result of breathing, speaking, sneezing, coughing, or vomiting, so they are always present in our breath, but speaking and coughing increases their number.<unk>  sizes range from < 1 µm to 1000 µm, and in typical breath there are around 100<unk> s per litre of breath. So for a breathing rate of 10 litres per minute this means roughly 1000<unk> s per minute, the vast majority of which are a few micrometres across or smaller. As these<unk> s are suspended in air, they are all by definition aerosols. However, large<unk> s (larger than about 100 µm, but depending on conditions) rapidly fall to the ground or another surface and so are only briefly suspended, while<unk> s much smaller than 100 µm (which is most of them) fall only slowly and so form aerosols with lifetimes of minutes or more, or at intermediate size, may initially travel like aerosols but at a distance fall to the ground like<unk> s ("jet riders"). As the<unk> s are so small they dry rapidly once in the surrounding air, shrink, and therefore remain suspended for a longer time (see airborne transmission). These<unk> s can contain infectious bacterial cells or virus particles they are important factors in the transmission of<unk>  diseases. In some cases, in the study of disease transmission a distinction between what are called<unk> s" and what are called "aerosols" is made, with only larger<unk> s referred to as<unk> s" and smaller ones referred to as "aerosols" but this arbitrary distinction has never been supported experimentally or theoretically, and is not consistent with the standard definition of an aerosol.
Respiratory droplet
Dental aerosol
Airborne 
Inhalation
Dental instrument
Ventilated cigarette
Cigarette
Snuff 