Cf. Clement et Ij. Ford, Gas-to-particle conversion in the atmosphere: II. Analytical models of nucleation bursts, ATMOS ENVIR, 33(3), 1999, pp. 489-499
Simple models are developed to describe the formation of particles from con
densable vapours in different atmospheric circumstances. The models are des
igned for use in large scale global transport models, where sub-grid descri
ptions are required for such phenomena. We solve the evolution equation for
the density of a condensable vapour. When the concentration of existing ae
rosol is low, nucleation can occur, but only in intermittent, isolated burs
ts. In the absence of an initial aerosol, two analytical expressions are ob
tained for the number of particles produced in such bursts, valid for high
and low rates of vapour production, respectively. These results compare fav
ourably with calculations made using a detailed numerical code, using the h
omogeneous nucleation of sulphuric acid/water droplets as an illustration.
Then we consider barrierless nucleation, where clusters are always stable a
gainst evaporation, which is relevant to the production of ammonium sulphat
e particles in the atmosphere. We go on to consider conditions where existi
ng aerosol can affect the production of particles, and also consider slower
bursts where the time dependence of the vapour production rate, and not co
ndensation on the nucleated aerosol, cuts off nucleation. (C) 1998 Elsevier
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