Lack of Salty Rainwater
Why doesn't water from the ocean fall as salty rain?
Actually, much of the rain that falls near a coastline
has salt in it. Salt is an excellent nucleus for water
vapor to form a rain drop on. However, since a lot of
water is contained in a raindrop, it dilutes the salt
nucleus to the point that it's hard to tell that there
is salt in the drop. The rain drop is not nearly
as salty as seawater.
David R. Cook
Climate Research Section
Environmental Science Division
Argonne National Laboratory
When water evaporates from the oceans, the salt is left behind. There are
lots of microscopic salt particles in the atmosphere however, as water
droplets from waves evaporate. These same salt particles become
condensation nuclei for raindrops and snowflakes. The salt quantity in the
raindrops is so small that the raindrops are considered fresh water. There
are other kinds of condensation nuclei besides salt particles, such as
dust, volcanic ash, even ice crystals, and other chemical particles that
attract water vapor.
Wendell Bechtold, meteorologist
Forecaster, National Weather Service, Retired
Weather Forecast Office, St. Louis, MO
The salt dissolved in ocean water does not exist in the vapor, so only
water evaporates, in a calm ocean. Now if the turbulence is great enough,
caused by winds and waves some salty water does get "splashed" into the
air and will be incorporated into rain, but this is a small effect
compared to the vaporization of pure water from ocean water.
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Update: June 2012