generation of maritime cloud condensation nuclei (CCN) through
the ejection of jet and film droplets from bursting whitecap-produced
bubbles on the ocean surface has been well documented. The
processes involved in the transformation (evaporation and
crystallization) of these liquid droplets into their solid
form under varying conditions, however, has not previously
attracted much attention from atmospheric researchers.
A set of laboratory investigations and field observations
of the characteristics, both physical and chemical, of seawater
droplets during phase change in a controlled environment have
revealed the following startling and very significant phenomena:
The ejection of sulfate aerosols (CaSO4,MgSO4) with size range
of 0.1mm to 10 mm. The concentration and chemical composition
of the ejected aerosols, identified by the techniques of scanning
electron microscopy and energy dispersive x-ray spectroscopy,
were dependent on the rate of droplet evaporation. Sea-salt
aerosols could be classified into three categories: (A) NaCI
crystals, (B) Crystals of sulfates (CaSO4,MgSO4) and (C) Chloride
droplets (MgCI2, KCI).
The formation of hollow spherical sea-salt particles (>5 mm).
A secondary ejection of aerosols was detected during melting
by the busting of air bubbles, which were formed when the
hollow particle was moved into a high-moisture environment
or dissolved into a water droplet.
A thin film of chlorides (MgCl2, KCI) observed on the surface
of sea salt particles present a highly hygroscopic surface
to initiate the condensation of water vapor in an environment
with RH As low as 40%. Sodium Chloride (NaCI-75%RH) plays
only a minor role for the formation of cloud droplets in the
of the ejected sulfate aerosols in comparison with field observation,
chemical processes inside the evaporating seawater droplets
and the mechanisms for the generation of secondary aerosols
in the marine atmosphere are presented with illustrations.