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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 material is replicated on a number of sites as part of the SERC Pedagogic Service Project


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.

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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.

    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) PRIVATE FILE 168kB Aug22 04) for easy printout;
  • the CFC activity in MS Word format (Microsoft Word PRIVATE FILE 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) PRIVATE FILE 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.

  • Subject

    Environmental Science:Policy:Global Policy, Environmental Science:Global Change and Climate:Ozone depletion, Geoscience:Atmospheric Science:Meteorology:Atmospheric structure and composition

    Resource Type

    Activities:Lab Activity, Datasets and Tools:Datasets with Teaching Activities

    Special Interest

    Data, models, or simulations:Data, Quantitative

    Grade Level

    College Lower (13-14):Introductory Level

    Quantitative Skills

    Graphs, Probability and Statistics:Describing Data Distribution, Models and Modeling

    Ready for Use

    Ready to Use:Meets Peer Review Standard:Anonymous Peer Review, Ready to Use

    Earth System Topics

    Climate, Atmosphere, Human Dimensions:Policy


    Teach the Earth:Teaching Topics:Weather, Teach the Earth:Teaching Environments:Intro Geoscience, Teach the Earth:Course Topics:Environmental Science, Atmospheric Science, Teach the Earth:Incorporating Societal Issues:Climate Change, Public Policy