From AMS Glossary
The study of the distribution of living organisms freely suspended in the atmosphere and some consequences of this distribution.
It includes microorganisms and some insects, seeds, and spores. Dispersion is by the wind, aided in some species by special adaptations and in some by flight. Small organisms are lifted and maintained in the air by eddy diffusion and rising thermal currents, sometimes reaching heights exceeding 16 km (10 miles) in air currents and by lateral mixing. They may be collected by adhesive-coated slides exposed horizontally, or by culture media, but for quantitative work, volumetric sampling at the surface or by aircraft is required.
Jacobs, W. C. 1951. Compendium of Meteorology. 1103–1111.