Video Transcript
How thick would the layer of 300
Dobson units of pure atmospheric ozone at the surface of Earth be?
Ozone is a gas that is formed in
the highest concentrations within the stratosphere, the second layer of atmosphere
above the Earth’s surface. The highest concentrations of this
gas are found at an altitude of between 20 kilometers and 40 kilometers. The exact concentration of ozone
depends upon the precise altitude and the location above the Earth’s surface. It varies from place to place.
To measure the concentration of
ozone gas at a particular location on Earth, we can use the Dobson unit. The Dobson unit is defined as the
thickness of the ozone layer in the column of air above a specific point. We could take all of the trace gas
ozone in a column of atmosphere extending from the Earth’s surface to the edge of
space. We would then concentrate all of
the ozone into a pure layer at sea level and normal atmospheric pressure. The thickness of this layer would
be established, as if it were under normal atmospheric pressure and at a temperature
of zero degrees Celsius. These conditions are known as
standard temperature and pressure.
At a concentration of one Dobson
unit in the atmosphere, a gas will give a layer of thickness 0.01 millimeters at the
Earth’s surface under these conditions. At a concentration of 300 Dobson
units, we can see that the thickness of the layer of pure ozone at the Earth’s
surface would be three millimeters. Three millimeters is the correct
answer to this question.
