Remember the warning to beware of yellow snow? Well, what’s true
in your backyard is true on a much larger scale too. (For those
from warmer climates, yellow-tinted snow is a sign that a dog or
other animal has recently “paid a visit.”) Snow at Earth’s north
and south poles can also be tainted. Certain molecules — ones
that can eventually damage our protective ozone layer in the
stratosphere, affect the air down in the troposphere where we
live, and possibly contribute to climate change — are being
deposited into the snow. Just how is this happening? Start with
the fact that air at lower latitudes circulates toward the
poles. This air carries ozone-damaging molecules picked up in
industrial, highly populated areas. Once over the poles, some of
these molecules are deposited onto the snowpack, where they
migrate to thin liquid films in snow. Once sunlight hits the
snow, the light energy breaks down these molecules, which are
then released back into the atmosphere, giving the area over the
poles a double hit of