Earth History

Page
7

Ozone Layer

Ozone (O3)

Chlorine monoxide ClO.

Chlorine monoxide ,ppb

Ozone, ppm

1.0

0

2.5

0.5

Latitude

63oS

73oS

Slide 52

Thickness of Ozone Layer

The thickness of the Ozone Layer is expressed in Dobson units (DU) and is equivalent to 0.001 mm thickness of pure O3 at the density it would possess at ground level (1 atm)

Equator = 250 DU

Temperate Latitudes = 350 DU

Subpolar regions = 450DU

Slide 53

Other Ozone Depleters

But has the reduction and removal of CFC’s solved the problem of the Ozone Hole ?

Or could there be other causes that are producing the Ozone Hole. ?

Could our pollution arising from NO2 and CO2 contributing factors ?

Slide 54

Interactive Catalytic Forms

Destruction: Halide Radicals destroy Ozone.

The majority of Chlorine does not exit as Cl. or ClO The two major nonradical inactive as catalysts species in the Stratosphere are:

HCl Hydrogen chloride

ClONO2 Chlorine nitrate gas

Slide 55

Interactive Catalytic Forms

Formation of nonradical chlorine species.

ClO. + NO2. ClONO2

Cl. + CH4 HCl + CH3.

But HCl react with Hydroxyl Radical

HCl + OH. H2O + Cl.

( ClO. & Cl. Catalytically Active )

Slide 56

Origin of Ozone Hole

The major destruction of the hole in the lower atmosphere occurs as a result of special winter weather conditions when the chlorine stored as the catalytically inactive forms (HCl & ClONO2 ) are converted to the catalytically active forms (ClO. & Cl.)

(This occurs in Polar Stratospheric Clouds)

Slide 57

Ice crystal formation

Nitric acid in the atmosphere forms from the reaction between OH.& NO2.

Catalytically inactive to active chlorine occurs on the surface of ice crystals formed from water and nitric acid in the lower stratosphere in winter when the temperature drops to

 -80oC over the South Pole.

Slide 58

Possible Role of CO2

“ CO2 acts as a blanket in the lower atmosphere,” says Salawitch. “ To balance the books the Stratosphere has to cool”

Thus CO2 could be contributing to helping PSC formation due to reduced temperatures in the stratosphere.

New Scientist, 1 May 1999 p28

Slide 59

Impenetrable Vortex formation