Supplementary videos

Ozone hole peaks over Antarctica (2008)
Dragonflies that cross oceans: simple observations lead to breathtaking discoveries

Extra credit readings

• Greener, HFC-free refrigerator set to enter U.S. market in 2011 Washington Post 12/26/10
• EPA Approves Hydrocarbon Refrigerants for Commercial and Household Use Environment News Service 12/15/11

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