Aerobiology is a branch of biology that studies airborne organisms and airborne biological particles, for example, pollen and spores.
In 2002, algae and other small water-borne organisms were discovered to inhabit clouds. A large cloud has about as much water as a shallow lake of the same geographic size.
An important medical application of aerobiology is the study of the transmission of airborne diseases. It is known that many bacteria and viruses can be transmitted by spread through the air, possibly within droplets. In addition, biological warfare agents can be transmitted in this manner, and therefore this field is of interest in that application.