A variety of bioaerosols may contribute to cloud condensation nuclei or cloud ice nuclei, possible bioaerosol components are living or dead cells, cell fragments, hyphae, pollen, or spores. Cloud formation and precipitation are key features of many hydrologic cycles to which ecosystems are tied. In addition, global cloud cover is a significant factor in the overall radiation budget and therefore, temperature of the Earth.
Bioaerosols make up a small fraction of the total cloud condensation nuclei in the atmosphere (between 0.001% and 0.01%) so their global impact (i.e. radiation budget) is questionable. However, there are specific cases where bioaerosols may form a significant fraction of the clouds in an area. These include:
* Areas where there is cloud formation at temperatures over -15 °C since some bacteria have developed proteins which allow them to nucleate ice at higher temperatures.
* Areas over vegetated regions or under remote conditions where the air is less impacted by anthropogenic activity.
* Near surface air in remote marine regions like the Southern Ocean where sea spray may be more prevalent than dust transported from continents.
The collection of bioaerosol particles on a surface is called deposition. The removal of these particles from the atmosphere affects human health in regard to air quality and respiratory systems.