Environmental Engineering Reference
In-Depth Information
Chapter 2
Atmospheric Biogeochemistry
Natalie M. Mahowald
Glossary
Aerosol
A solid or liquid suspended in the atmosphere. The definition
usually does not include cloud droplets, although many aerosols
have water vapor on their surfaces.
Dry deposition
Removal process for gas and aerosol species in which the species
are deposited onto the lower surface due to either turbulent fluxes
(overturning air) forcing the constituent to hit and stick to
the surface, or from gravitational settling of aerosols. Gravita-
tional settling is the dominant mechanism for removal for larger
aerosols.
Lifetime
The atmospheric lifetime of a constituent describes how long the
constituent will remain in the atmosphere. It is typically calcu-
lated by dividing the total amount of the constituent in
the atmosphere by the total flux out of or into the atmosphere.
The flux can be due to atmospheric chemical reactions, and/or
exchanges between other reservoirs in the earth system (e.g., land
or ocean). This lifetime is an e-folding lifetime; if one starts with
an initial perturbation of the constituent, the amount of the pertur-
bation remaining after a length of time equal to the lifetime is
equal to 1/e of the original value of the perturbation.
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