PS10.1: Average O3 Concentration

1
PS10.1 Average O3 Concentration

2
PS10.2 O3 Residence Time

• The short residence time of O3 helps explain why
  O3 holes can develop and disappear so rapidly.
  Systems with short residence times respond very
  quickly to perturbationsin this case, O3 drops
  rapidly during the start of the Antarctic spring
  as free Cl destroys O3, and rises rapidly as
  these reactions drop off and O3 production picks
  up. If we could get rid of the Cl, the O3 layer
  would be fine. Unfortunately, Cl has a long
  residence time in the stratosphere, so even if we
  stop CFC emissions entirely, the destruction of
  ozone will continue for decades until the Cl is
  removed.

3
PS10.3 O3 Destruction by CFC-11

• If production continues at a constant rate, then
  eventually production flow into stratosphere
  breakdown into free chlorine, and the
  steady-state rate of O3 destruction is

4
PS10.3 O3 Destruction by CFC-11

• (0.86)(440,000) (0.9)(140,000)
• (5.1)(2,600) (12.5)(2,600) (0.05)(81,200)
  (0.12)(500,000) (1.2)(70,000)
• 700,000 t/yr CFC11 equivalent
• So the total production of these compounds has
  the ozone-destroying potential equal to
  production of 300,000 700,000 1 MtCFC11.
• Redoing the above calculation, this would lead
  to the destruction of about 4?1038
  molecules(O3)/y.

5
PS10.3 Reduction in O3 Stock

• Before CFCs, the natural destruction of ozone
  equaled the rate of production, 2?1039 O3/y.
• After CFCs, production remains unchanged. (As
  noted in class, that depends only on the flux of
  solar radiation and the concentration of O2, both
  of which are fairly constant.
• The natural destruction of ozone, on the other
  hand, is dependent on the concentration of ozone.
  In other words, the residence time of O3 with
  respect to natural destruction remains constant.

6
PS10.3 Reduction in O3 Stock

• P natural rate of O3 production (constant)
• So natural O3 stock S S after CFCs
• ? residence time for natural O3 destruction
• D rate of O3 destruction due to CFCs
• Before
• After

20 reduction
7
PS10.3D Reduction in O3 Stock

• Before
• After

17 reduction