Sea salt aerosols
Sea salt aerosols are tiny airborne droplets of sea water, or salt-rich particles
formed by the evaporation of water from such droplets. Physical processes occuring
at the surface of the ocean inject large quantities of aerosol particles into
the troposphere. The primary pathway of creation is the bursting of air bubbles
during whitecap formation and wave breaking. When bubbles burst, a small jet
of water forms that can eject droplets up to 15 cm above the water surface.
Not surprisingly, the strength of the ocean as a source of salt particles
depends on wind speed. Sea salt aerosol is optically very important at wind
speeds above 7 to 10 m s-1. This aerosol may be the dominant contributor
to both light scattering and cloud nuclei in those regions of the marine atmosphere
where wind speeds are high and/or other aerosol sources are weak.
Sea salt particles cover a wide size range belong to the coarse particle size
mode. Sea salt aerosols occupy a wide size range (ca. 0.05-10 µm diameter),
and have a correspondingly wide range of atmospheric lifetimes. Chemically,
these aerosols are comprised mainly of NaCl, KCl, CaSO4, (NH4)2SO4.
They are hygroscopic - able to attract water from the air. Thus the size of
the particles varies with humidity.
Total sea salt flux from ocean to atmosphere is estimated to be 3300 Tg/yr
(IPCC).