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== Dispersal of particles == The process of dispersal of aerobiological particles has 3 steps: removal from source, dispersion through air, and deposition to rest.<ref name=":1">{{Cite journal |last=McCartney |first=H. Alastair |date=April 1994 |title=Dispersal of spores and pollen from crops |journal=Grana |language=en |volume=33 |issue=2 |pages=76β80 |doi=10.1080/00173139409427835 |doi-access=free |bibcode=1994Grana..33...76M }}</ref> The particle geometry and environment affect all three phases, however once it is aerosolized, its fate depends on the laws of physics governing the motion of the air. === Removal from Source === [[file:puffballs emitting spores.jpg|thumb|A puffball mushroom ejecting its spores.]] Pollen and spores can be blown from their surface or shaken loose. Generally the wind speed required for release is higher than average wind speed.<ref name=":1" /> Rain splatter can also dislodge spores. Some fungi can even be triggered by environmental factors to actively eject spores.<ref name=":1" /> === Dispersion through Air === Once released from rest, the [[aeroplankton]] is at the mercy of the wind and physics. The settling speed of spores and pollen vary and is a major factor in dispersion; the longer the particle is floating, the longer it can be caught by a turbulent wind gust. Wind speed and direction fluctuate with time and height, so the specific path of once neighboring particles can vary significantly.<ref name=":1" /> The concentration of particles in the air decreases with distance from source, and the dispersion distance is most accurately modeled as a [[Power Function|power function]].<ref name=":4" /> === Deposition to Rest === Deposition is a combination of gravity and inertia. The fall speed for small particles can be calculated by mass and geometry, but the complex shapes of pollen and spores often fall slower than their estimated speed modeled with simple shapes.<ref>{{cite journal |last1=Sabban |first1=Lilach |last2=van Hout |first2=RenΓ© |title=Measurements of pollen grain dispersal in still air and stationary, near homogeneous, isotropic turbulence |journal=Journal of Aerosol Science |date=December 2011 |volume=42 |issue=12 |pages=867β882 |doi=10.1016/j.jaerosci.2011.08.001 |bibcode=2011JAerS..42..867S }}</ref> Spores can also be removed from the air from impact; the inertia of the particles will cause them to hit surfaces along their path, instead of flowing around them like air.<ref name=":1" />
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