Earth History

Page
8

The usual warming mechanism from of O + O2 O3 + Heat

is absent due to total darkness and the stratosphere becomes very cold. As a result the air pressure drops ( PV=nRT ) and due to the rotation of the earth an impenetrable vortex forms with winds up to 300km/hr

Slide 60

PSC’s

Matter cannot readily enter this vortex and the air inside is isolated and remains cold for many months. ( Mid October)

The crystals formed by the condensation of the gases within the vortex form

Polar Stratospheric Clouds which consist of crystals of trihydrate of Nitric Acid.

Slide 61

HCL attachment

Gas phase HCl attaches to the ice particle

Crystal

HNO3.3H2O

of

HCl

HCl

HCl

HCl

HCl

HCl

Ice Particle

formed at low

Temperature

(-80oC)

Slide 62

Role of ClONO2

Ozone Layer (Radicals in PSC)

Crystal

HNO3.3H2O

of

HCl

HCl

HCl

HCl

HCl

HCl

ClONO2

Cl2

ClONO2 collides with HCl to form Molecular Chlorine

Accumulates

in Winter

Slide 63

Formation of Cl. Radicals

Ozone Layer (Radicals in PSC)

Crystal

HNO3.3H2O

of

HCl

HCl

HCl

HCl

HCl

HCl

ClONO2

Cl2

Cl.

Cl

When the Light in Summer appears Cl2 is converted to Cl.

UV light

Summer

Accumulates

in Winter

Slide 64

Hole Closure

ClONO2(g) also reacts with water

H2O(s) + ClONO2(g) HOCl(g) +HNO3(s)

HOCl + UV light OH. + Cl.

It is only when the vortex has vanished does chlorine predominate in its inactive forms and the hole closes.

Slide 65

Dimer ClOOCl

ClO. also builds up in the dark and this dimerizes to for a relatively stable species.

ClO. + ClO. ClOOCl

When the Sun Appears

ClOOCl 2 Cl. + 2O.

Which contributes to Ozone destruction.

Slide 66

Antarctic and Arctic Vortexes

Ozone Layer (PSC’s)

The Antarctic vortex is more intense than the Arctic which is more sensitive to temperature.

The Arctic vortex is broken down more readily by rise of planetary waves created when air flows over mountains.

Current research is using a U2 type aeroplanes to probe PSC’s

Slide 67

Possible Link

Ozone Layer