Video Transcript
In September of each year in the
Antarctic, the rate of ozone destruction increases. Why does the formation of these
Antarctic ozone holes occur during September? (A) September is springtime in the
Antarctic, and a lot of methane gas is created by animals coming out of
hibernation. (B) September is springtime in the
Antarctic, and sunlight reaches the region. (C) September is summertime in the
Antarctic, and the region receives more sunlight. (D) September is fall in the
Antarctic, and the fishing season brings many boats that pollute the ice. (E) September is a busy industrial
period for Argentina, Australia, and South Africa, and levels of air pollution
increase.
The question asks us to identify
why ozone holes form over Antarctica during the month of September. Let’s clear some space to think
about this question. During the Antarctic winter, much
of Antarctica is in darkness for days to months. This is because of the tilt of the
Earth’s axis and its position in its orbit around the Sun. Antarctica points away from the Sun
during its winter and is in shadow. However, when September arrives,
the Earth has moved a bit in its orbit, and now sunlight begins to reach the
region. It is springtime in Antarctica.
Let’s have a closer look at what
happens here. Incoming ultraviolet radiation from
the Sun interacts with chemical pollutants in the air above the Antarctic. The energy from the UV radiation
causes chemical reactions to occur, which destroy ozone molecules. As a result, the concentration of
ozone begins to decrease. We call thinning of the ozone layer
ozone holes. Ozone holes are not really holes,
but areas of low or decreased ozone concentration. Now, we mustn’t get confused. UV radiation from the Sun reaches
much of the atmosphere year-round. And chemical pollutants, which are
harmful to the ozone layer, exist throughout the atmosphere, not just above
Antarctica.
So, why then do ozone holes form
over the Antarctic specifically? Well, it is not just the
combination of UV radiation and chemical pollutants, which destroy ozone. It is, in fact, the unique
combination of UV radiation, chemical pollutants, as well as the low cloud cover and
very cold temperatures above the Antarctic, which create the conditions which cause
a high rate of ozone destruction.
Now we know how ozone holes form,
let’s bring back the answers. Why do ozone holes form in
September above the Antarctic? The answer is (B): September is
springtime in the Antarctic, and sunlight reaches the region.
