California State University, Long Beach
Department of Geography
Introductory Physical Geography Lab
The Ozone Hole over Antarctica
Introduction
In this lab, you will graph two measures of the ozone hole, which develops over Antarctica in its early spring (September and October). A similar, though smaller and less intense phenomenon has begun to take place over the Arctic since the late 1990s, by the way. If you would like to know more about atmospheric ozone, you can read the Stratospheric Ozone Electronic Textbook at http://www.ccpo.odu.edu/SEES/ozone/oz_class.htm. This is a resource developed by NASA's Goddard Space Flight Center Atmospheric Chemistry and Dynamics Branch (Code 916). A more basic description of the situation can be found at The Ozone Hole Organization's web site, http://www.theozonehole.com/. A K-12 educator's site created by the University Corporation for Atmospheric Research offers a simple graphic and an animation showing how chlorofluorocarbons (CFC's) lose chlorine atoms when they're hit with ultraviolet energy and then disrupt ozone over and over, producing the ozone hole: http://www.ucar.edu/learn/1_6_2_25t.htm.
Objectives of this lab:
- to convey the dramatic change in this phenomenon in a really very short time, less than three decades, so that you appreciate why scientists are so concerned.
- to give you practice in the construction of a type of X-Y graph called a "frequency polygon," which is very commonly used for graphic communication of data in the sciences. Those in this lab are time series, that is, they have year on the X (or horizontal) axis. The Y (or vertical) axis is some measure of the ozone hole phenomenon (for the first graph, that would be minimum recordings each year and, for the second, spatial extent of the ozone hole).
- to familiarize you with a unit of measure designed for recording variations in ozone amounts in the air above a given place (Dobson Units).
- to give you practice in turning graphs into meaning: at the end of the lab, you will write a brief lab report summarizing the trends in your graphs.
Antarctic Annual Minimum Ozone Values
Plot each year's minimum ozone reading over Antarctica over the course of 29 years (1979 through 2007) onto the graph paper provided here.
The readings are given in Dobson Units (DU). A Dobson Unit is all the ozone in a column of air squashed onto the surface at sea level (in other words, at 1 "standard atmosphere" of air pressure) and corrected for a constant temperature (0° C). The correction is because, the warmer a substance is, the more motion is going on among its molecules and the less tightly they can pack together, which would affect a thickness-based measure like this. What you're trying to imagine is grouping all the ozone molecules at the bottom of the imaginary column of air, which means you have to move the other air molecules that were there before up higher to make room for the ozone molecules at the bottom of the air column. Then, you chill (or warm) the ozone to a nice, even 0° C. When you've done all that, you measure the thickness of the layer, at least conceptually. Anyhow, a layer of corrected ozone 1 mm thick is 100 DU (1 mm is the diameter of the wire making up the common paper clip).
An ozone hole condition occurs whenever ozone drops below 220 DU. In fact, minimum levels below 220 DU were not seen in Antarctica before 1979 (ozone readings have been taken there since the 1950s). Normal ozone levels are somewhere around 300 DU. They were normal in the Antarctican spring, averaging around 300 or even higher, before about 1968 and even then averaged above about 250 until about 1979. In fact, when the first low readings started coming in during the 1970s, scientists assumed the instruments were faulty or someone was messing up their job reading them! It took a few years, until about 1979, before everyone realized something very real and very negative was going on down there. What you're to plot are each year's record low ozone levels, or annual minima (not the monthly averages) from that time forward.
To do this part of the lab, you need to print the graph paper above, which you'll find already has pre-marked axes and a legend. What you do is look up each year in the table below and then on the X axis. Put a dot on the graph exactly above the year and precisely to the right of the ozone reading. If you drew faint lines straight up from the year and straight across from the ozone reading, your dot should be exactly where the two faint lines cross.
After you have all your dots, then connect each year's dot with the next one (or, in the case of 1994, with 1996, since there are no data for 1995) with a straight line (use a ruler). Voilà! -- your frequency polygon.
Be sure to put your name on it! Always enhances the grading experience!
Antarctic Ozone Minimum Values Over Time
60° - 90° S
September-October minima from 1979 through 2007
Measurement in Dobson Units (DU)
Instrument: Total Ozone Mapping Spectrometer (TOMS), 1979-2004 and Ozone
Montoring Instrument (OMI), 2005-2007
Source: NASA Goddard Space Flight Center data published at the NASA
Goddard Space Flight Center Ozone Hole Monitoring page:
http://macuv.gsfc.nasa.gov/ozone.md Estimated years from graphs on
http://ozonewatch.gsfc.nasa.gov/
Minimum Minimum
Ozone Ozone
Year (DU) Year (DU)
______________ ______________
1979 194 1994 80 (est)
1980 192 1995 no satellite in place
1981 195 1996 103
1982 177 1997 99
1983 154 1998 86
1984 144 1999 97
1985 124 2000 89
1986 140 2001 91
1987 109 2002 131
1988 162 2003 91
1989 108 2004 102
1990 111 2005 102
1991 94 2006 83
1992 105 2007 107
1993 100 (est)
Average Spatial Extent of the Ozone Hole over Antarctica
Plot the spatial extent of the ozone hole over Antarctica over the course of the 29 years (1979 through 2007). Use the graph paper provided here.
The ozone hole is defined as the area poleward of the 220 DU isoline (hey, no-one's named that isoline -- how 'bout we call it an "isodobson"? -- you read it here first <G>!). So, "isodobsons" are plotted from satellite data (the Total Ozone Mapping Spectrometer [TOMS] carried on the Nimbus-7 satellite from 1979 through 1992, then on the Meteor-3 satellite from 1993-94, and then on the Earth Probe satellite from 1996 to 2004; and, since 2005, the Ozone Monitoring Instrument carried on the EOS-Aura satellite). The area falling within the 220 "isodobson" is the ozone hole.
You can view this area as it develops over the South Pole this year and last year in a series of animations mapping the Dobson Unit gradient for every day from the 1st of July through the 2nd of October. There are also October monthly averages for each year from 1979 to 2007. The boundary between the aqua shaded areas and the blue areas coïncides with the 220 "isodobson." So watch the areas mapped in blue, purple, and violet that develop over the South Pole: These colors show the ozone hole, where aqua and green show the normal ozone levels.
NASA-Goddard's Ozone Watch site
The size of the area within the 220 "isodobson" is reported in the table below in millions of square kilometers. So, again, print out a copy of the graph paper provided and put your name on it. Again, the X axis shows each of the 29 years, and the Y axis is size of the ozone hole in millions of square kilometers.
What you do is look for each year, starting with 1979, against the left side of the graph. Put a dot on the graph perfectly above the tick mark for that year at the level exactly to the right of the size of the ozone hole area. I've generalized the ozone hole area to the nearest 1 million square kilometers, so you can pinpoint the reading for a given year as easily as possible with reference to the tick marks. Again, you are trying to create cross-hairs between a perfectly vertical line above the year and a perfectly horizontal line across from the ozone hole area reading, and you put a dot at the intersection between them.
Just as you did with the previous graph, go back and mark a straight line connecting each year's dot with the one before it and the one after it (skipping straight from 1994 to 1996, of course). There you are: your second frequency polygon.
Average Area of ozone hole over time
Data generalized by C.M. Rodrigue from NASA Goddard SFC
at http://macuv.gsfc.nasa.gov/ozone.md
Area bounded by the 220 DU isoline
September - October from 1979 to 2007
Ozone Hole Ozone Hole
Area Area
Year (million km2) Year (million km2)
_________________ _________________
1979 0 1994 24
1980 2 1995 no satellite in place
1981 1 1996 24
1982 7 1997 23
1983 10 1998 26
1984 12 1999 23
1985 16 2000 27
1986 13 2001 25
1987 21 2002 15
1988 11 2003 27
1989 20 2004 20
1990 19 2005 24
1991 19 2006 27
1992 23 2007 23
1993 25
Brief Lab Report
On a separate sheet of paper with your name on it, write a brief analysis of the patterns you see in the two graphs, making sure to integrate the two patterns together. Basically, you are stating what the two graphs mean in the simple, clear English you would use to tell a friend what you learned in class today! Add a few comments relating the meaning of these two graphs to the classroom discussion of the composition of the atmosphere and why ozone is an important trace gas. This essay can easily be taken care of in one or two paragraphs.
This document is maintained by © Dr.
Rodrigue
First placed on the Web: 10/07/00
Last Updated: 10/04/08