Gravitational Settling

Microbes and Atmosphere
Part - I
Relationship between Microbes and Atmosphere
Atmosphere as a Habitat
Transport of Spores
Sampling of Air
Launching
Transport of Microorgannisms in Air
Deposition and Adhesion
Types of Deposition
Gravitational Settling
Surface Impaction
Rain and Electrostatic Deposition
Methods of Air Sampling
Impingement
Impaction
Centrifugation
Filtration and Deposition
Sampling Methods and their characteristics

Gravitational Settling

Gravitational Settling
The force of gravity acts upon all particles heavier than air, pulling them down asnd essentially providing spatial limitations on the spread of airborne particles. Gravitational settling is the function of the earth's gravitational pull, particle density, particle diameter and viscosity of air. Depicts the schematic representation of gravitational setting.

Downward molecular diffusion is a randomly occurring process caused by natural air currents that promote the downward movement of airborne particulates (in still as well as turbulent air). Molecular diffusion is also influenced by the force of wind.

Shows the schematic representation of downward molecular diffusion, a naturally occurring process caused by the air currents that promote and enhance gravitational settling of airborne particles. Although molecular diffusion can occur in any direction, due to the effects of gravity, the overall trend of the process results in net downward movement and deposition.

Schematic Representation of Downard Molecular Diffusion of Air

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