Polar Stratospheric Clouds (PSCs)
qIn winter the polar stratosphere
is so cold (-80°C or
below) that certain trace atmospheric constituents can condense.
qThese
clouds are called “polar stratospheric clouds” (PSCs).
qThe particles that form
typically consist of
a mixture of water and nitric acid (HNO3).
qThe PSCs alter the chemistry of
the lower
stratosphere in two ways:
q (1) by slow down the
coupling between
the odd nitrogen and chlorine cycles
q (2) by providing surfaces
on which heterogeneous
reactions can occur.
(Sweden, January 2000; from NASA website)