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Using Mass Balance to Understand Atmospheric CFCs

Activity and Starting Point page by R.M. MacKay. Clark College, Physics and Meteorology.
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This activity was selected for the On the Cutting Edge Reviewed Teaching Collection

This activity has received positive reviews in a peer review process involving five review categories. The five categories included in the process are

  • Scientific Accuracy
  • Alignment of Learning Goals, Activities, and Assessments
  • Pedagogic Effectiveness
  • Robustness (usability and dependability of all components)
  • Completeness of the ActivitySheet web page

For more information about the peer review process itself, please see http://serc.carleton.edu/NAGTWorkshops/review.html.

This page first made public: Sep 8, 2006

This material was originally created for Starting Point:Introductory Geology
and is replicated here as part of the SERC Pedagogic Service.


Students use an interactive online mass balance model to help understand the observed levels of chlorofluorocarbon CFC-12 over the recent past. They then explore the influence of post Montreal Protocol emission scenarios on future CFC levels and discuss the relevance of this to stratospheric ozone recovery.

Learning Goals

  • Use a model to estimate the future concentrations of CFC-12 under several different assumed emission scenarios.
  • Learn how a mass balance model applies to the global atmosphere.
  • Understand how atmospheric lifetime is related to the response time of atmospheric constituents.
  • Calibrate a model with recent observations.
  • Synthesize results into a well written summary.
  • Accurately read graphical information.
  • Read and interpolate data from a table of values.
  • Context for Use

    This activity is useful in any course with a section on atmospheric trace gases and/or stratospheric ozone. It has been used successfully in an introductory meteorology course as well as an upper division course on Earth's Climate for non-majors.

    Description and Teaching Materials

    The CFC Activity Page has links to:
    • the CFC activity in pdf format for students to printout and use;
    • the CFC model page so they can work through the activity.
    Here are:
  • the CFC activity in pdf format (Acrobat (PDF) 168kB Aug22 04) for easy printout;
  • the CFC activity in MS Word format (Microsoft Word 78kB Aug22 04) for easy editing;
  • Teaching Notes and Tips

  • This activity takes about 2-hours to complete.
  • This activity works best with a PC, but with proper configuration also works on MAC OS X.

  • Little mathematical background is required to complete this activity.
  • Here are some suggestions for effective classroom use and more details of the mathematics behind the model.
  • Also see References and Resources below.
  • Assessment

  • Grading the completed activity sheet provided below can be used as an assessment of student understanding. Follow-up discussions in class, essay questions on exams, and the future success of students on other related activities are also useful measures of student understanding.
  • Answers for CFC activity (Acrobat (PDF) 176kB Aug22 04)
  • References and Resources

    The activity "Using Mass Balance to Understand Atmospheric Levels of CFCs" described here is the third part of a four part learning module that I use in my courses when discussing Earth's Climate and Stratospheric Ozone.

    The first and second activities are:
  • Mass Balance using a water bucket model, introduces students to mass balance concepts using a water bucket model.
  • Trace Gases, is designed to extend the fundamental ideas and the terminology of mass balance into an atmospheric science context.

    If you are short on time you can highlight key aspects of these first two activities in a lecture and then assign one or both of the activities below.

  • These last two activities can be done in any order and use real data to address issues that are currently of interest to many students.