Geoscience Reference
In-Depth Information
cosmic rays give rise to the formation of aerosol particles and change the rate of
the aerosol processes such as nucleation, coagulation, and condensation (Castelman
1982
; Kulmala et al.
2004
; Harrison and Carslaw
2003
).
Recent modeling work by Yu and Turko (
2001
) indicates that small ions can
provide a source of atmospheric cloud condensation nuclei (CCN). The cloud
processes actively exerting the weather condition and climate occur within a weak
ionic plasma, susceptible to changes on all spatial and temporal scales. Coagulation
rates and the scavenging of aerosol particles from the atmosphere can be generally
affected by electric charging of aerosols. Many studies (Havnes et al.
1990
,
1992
,
1996
;Rapp
2000
;RappandLubken
1999
;YuandTurko
1998a
,
b
; Sorokin and
Mirabel
2001
; Sorokin et al.
2003
) have suggested that the charging processes
in the atmosphere play a key role in the formation of the aerosol state of the
atmosphere and especially its upper layers (Rapp
2000
;RappandLubken
1999
).
Such important effects, such as the reduction in electron density in the mesosphere,
can be caused by positively charged aerosol particles that appear consequent to the
aerosol photoeffect (Rapp and Lubken
1999
).
The particle charging is of key importance in the processes of formation of
aerosols from aircraft exhaust plumes. The dispersed and chemical content of
aerosols appearing in the atmosphere as a result of increasing air flight activity
strongly depends on the dynamics of charged particle formation in high-temperature
processes in aircraft motors (Yu and Turko
1998a
,
b
; Sorokin and Mirabel
2001
;
Sorokin et al.
2003
).
Of course, the significance of charged aerosol particles is not exhausted with their
atmospheric implications. Modern aerosol technologies of nanoparticle production
(Wen et al.
1984
; Adachi
1985
; Wiedenscholer and Fissan
1991
; Romay and Pui
1992
; Matsoukas
1997
; Smith et al.
1999
) widely apply charged aerosol particles
for modification of the particle-size distributions or for the regulation of the particle
content.
Aerosol electrification modifies aerosol deposition in the lungs (Hashish and
Bailey
1991
), including deposition of therapeutic aerosols. Domestic ionizers are
designed to release large quantities of negative ions, causing unipolar aerosol
charging. There are known biological effects of small ions. Harmful bacteria can
be killed or their growth inhibited by ions of both signs (Krueger and Reed
1976
).
The charging of aerosol particles is widely used for detecting fine aerosol
particles with sizes less than 0.1 m(Liu
1976
).
All kinetic models used for treating the effects just outlined demand knowledge
of the rates of elementary charging processes. Many authors addressed their efforts
to deriving the expressions for charging efficiencies of an aerosol particle by ions. It
is not difficult to resolve this problem for the continuous limit, where ion transport
is described by the diffusion equation (Reist
1984
;Smirnov
2000a
,
b
).
In the free molecule regime the charging efficiency can be easily found only when
the ion-particle interaction is described by the Coulomb potential alone. Attempts to
take into account the image forces make the analysis much more difficult. Especially
this concerns the dielectric particles, in which case the ion-particle interaction is
described by an infinite and slowly convergent series (Landau and Lifshits
1969
).
