The ozone hole is a bit of a misnomer since it is actually a decrease in the amount of ozone in the atmosphere, rather than an absence of ozone in the atmosphere. The amount of ozone in the atmosphere changes on a seasonal basis and is at its lowest levels in January, during Antarctic spring as the animation we created demonstrates. There is a correlation between ozone levels and atmospheric temperature. Ozone levels are measured in Dobson Units, a measurement of the thickness of pure ozone at normal sea level temperature and pressure. Thus, 100 DU equals 1 mm. of pure ozone at sea level.

### Find the hole in the ozone layer.

1. Determine a scale for the graph. Put time on the horizontal axis and Dobson Units on the vertical axis.
2. Graph the data on the ozone levels by either averaging every 10 days' worth of data or by graphing every 10th day. Discuss with students the advantage of either method as a way to reduce the number of data points.
3. According to the students' graphs, which time of year represents the lowest ozone concentration? Discuss possible reasons why.
4. Examine the satellite images of the ozone hole over the course of a year. Use the guidelines from the NIH Image activity that explains how to measure area with a computer program. Do the satellite images agree with conclusions reached from the graphs? What is the extent of the decreased concentrations of ozone in the atmosphere?
5. Discuss global actions that can reduce harmful impacts on the ozone layer.

### Materials

• graph paper
• satellite images that show the change in the ozone layer on a daily basis