The atmosphere has four main layers which are the troposphere (the lowest layer in which most weather occurs), the stratosphere, mesosphere, and thermosphere. There is some ozone in the troposphere, but it is a very small amount and is produced by the reaction of pollution and ultraviolet (UV) light. Most of the ozone in the atmosphere is located in the stratosphere, hence the name the “ozone layer”. The ozone layer is important because it filters out some harmful UV radiation. CFCs eventually make it into the stratosphere and mix in with the ozone molecules. The CFCs don’t do their damage until they react with UV radiation which breaks the bond of the chlorine or bromine atom apart from the rest of the CFC molecule. Chlorine and bromine are highly reactive with ozone (a molecule consisting of 3 oxygen atoms) which then breaks the ozone apart becoming a ClO and O2 (regular breathable oxygen). The creation of ozone in the stratosphere is from the interaction of UV radiation with an O2 molecule. It splits the O2 creating two single oxygen atoms which then react with O2 creating O3 (ozone).

Example of the CFC/Ozone destruction cycle from NOAA’s ESRL website

These appear to be processes that could take place all over the world so why is the ozone hole unique to the Antarctic region? There are two main factors that enable a hole in the ozone layer to form over Antarctica: the polar stratospheric vortex and polar stratospheric clouds. Antarctica’s extreme cold temperatures allow for these polar stratospheric clouds to form. The clouds enhance CFC/ozone reaction causing the destruction of ozone to become very effective. The polar stratospheric vortex forms every winter over the Antarctic continent and keeps the air from interacting outside of the vortex. So basically ozone from outside the vortex is unable to flow in and replenish during this time. That is when we see the lowest ozone values. As temperatures warm through the summer, the polar stratospheric vortex begins to break up, polar stratospheric clouds disappear, and the air mixes back into the Antarctic stratosphere replenishing the ozone layer. The filling in of the ozone hole causes a decrease in ozone worldwide which how it becomes a worldwide issue. The ozone hole hasn’t proved to be decreasing yet but the fact that the harmful CFCs look to be working their way out of the atmosphere is encouraging and we look for the hole to begin decreasing in decades to come.

So right now we are at the point where the sun is getting just high enough (still well below the horizon) that its rays are beginning to hit the stratosphere breaking down the CFCs that are up there. At the Atmospheric Research Observatory (ARO) we measure ozone in three different ways. One is with a surface analyzer that gives us a baseline level of tropospheric ozone, and the other two include the Dobson Spectrophotometer and launching ozonesondes which both give us an idea of stratospheric ozone.

Ozone surface analyzers

The Dobson Spectrophotometer. During the winter, observations are only available when the moon is up. Bad weather and poor visibility can hamper opportunities thus making balloon launches extremely important (especially so this winter it seems!).

For most of the year we launch one balloon a week but as the ozone hole forms we start launching two to three times a week. The idea is that we increase the resolution of the data so that we can see the peak of the ozone depletion. The balloons are great because they give us a complete profile of the ozone all the way up to 30-35 kilometers high.

In the winter we launch plastic balloons. The rubber balloons don’t get high enough due to the cold air. (ideally we like to get up to 28-30km).

When there is enough light outside for video, I will take you through an entire launch sequence explaining how we prep the sonde, prep the balloon, launch the balloon and show the software that gives us the profile of the data. We can even compare what a normal “healthy” layer looks like prior to the hole forming to the hole itself.