CFCS, CCI (parts per trillion - ppt) 4. CFC-11 at steady state At peak levels around...

 

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CFCS, CCI (parts per trillion - ppt) 4. CFC-11 at steady state At peak levels around the time of the Montreal Protocol, global CFC-11 (CC13F) emission rates were estimated at around 350 Gg year 1 (1 Gg = 109 g) and mixing ratios were measured at around 270 ppt (ppt = mixing ratio x 1012). Imagine a scenario where emissions were not reduced, but rather held fixed at those rates until CFC-11 achieved equilibrium. 600- 500- Northern Hemisphere Atmospheric Concentrations: CFCS, CCI and SF6 400- 300 200 100- a) CFC-11 has a lifetime of around 55 years. What would be its total steady state burden once it reached equilibrium? Now assume that emissions had been successfully reduced to exactly zero after these peak levels in 1990. 0 1940 b) Given its initial levels and lifetime above, calculate what mixing ratio would be expected 25 years later in 2015, assuming perfect exponential decay. How does this calculated value compare to actual CFC-11 measurements shown for 2015 below? c) What could explain the difference between your simplified calculation and actual measurements? 1960 CFC-12 CFC-11 1980 Year SF6 2000 12 10 -8 -6 -0 2020 SF6 (ppt) CFCS, CCI (parts per trillion - ppt) 4. CFC-11 at steady state At peak levels around the time of the Montreal Protocol, global CFC-11 (CC13F) emission rates were estimated at around 350 Gg year 1 (1 Gg = 109 g) and mixing ratios were measured at around 270 ppt (ppt = mixing ratio x 1012). Imagine a scenario where emissions were not reduced, but rather held fixed at those rates until CFC-11 achieved equilibrium. 600- 500- Northern Hemisphere Atmospheric Concentrations: CFCS, CCI and SF6 400- 300 200 100- a) CFC-11 has a lifetime of around 55 years. What would be its total steady state burden once it reached equilibrium? Now assume that emissions had been successfully reduced to exactly zero after these peak levels in 1990. 0 1940 b) Given its initial levels and lifetime above, calculate what mixing ratio would be expected 25 years later in 2015, assuming perfect exponential decay. How does this calculated value compare to actual CFC-11 measurements shown for 2015 below? c) What could explain the difference between your simplified calculation and actual measurements? 1960 CFC-12 CFC-11 1980 Year SF6 2000 12 10 -8 -6 -0 2020 SF6 (ppt)

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