Geoscience Reference
In-Depth Information
C
m
t*
t**
TIME
Fig. 3.1
Shown is the qualitative picture of the particle formation in the presence of a constant
in time source of low volatile vapors. At the initial period the concentration grows linearly with
time. At t
t
it begins to bend as the vapor concentration reaches a sufficiently high level for
the spontaneous nucleation process to start. Newly born particles appear and begin to consume the
vapor. The vapor concentration thus passes a maximum. The nucleation process stops at t
D
t
where the vapor concentration level drops lower than the critical value c
. At the postnucleation
stage the evolution continues mainly owing to the growth of the particles by simultaneous joining
the vapor molecules and the smaller nanometric particles to larger submicrometer ones. The period
of intense particle formation t
<t<t
is referred to as the nucleation burst
D
for example), the main difficulty of the route toward the final solution of this
problem has not been overcome. The point is that condensation efficiency is a rather
complicated function of particle size. Its exact form is not known, and instead the
interpolation formulas (see Seinfeld and Pandis
2006
; Friedlander
2000
; Williams
and Loyalka
1991
for a collection of such interpolations) are used in almost all
aerosol calculations. However, even the use of this semi-empirical approach does
not eliminate the necessity to introduce further approximations, based mainly on
the “isolated mode approximation,” where the particle-size distribution splits into
several narrow modes, each of which grows independently. The dynamics of the
nucleation modes is described within a lognormal theory (Lushnikov and Kulmala
2000
,
2001
).
Now it becomes more and more evident that the nucleation bursts in the
atmosphere can contribute substantially to cloud condensation nuclei production
and can thus affect the climate and the weather conditions on our planet (Charlson
and Heitzenberg
1995
; Kulmala et al.
2004
). Commonly accepted opinion connects
the nucleation bursts with an additional production of nonvolatile substances that
can then nucleate, producing new aerosol particles, or condense on newly born
