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From the Science Reviews archive: Effect of HCl addition and temperature on the hetrogeneous chemistry and photochemistry of ClONO2 adsorbed on ice crystals.

Posted on 24. March, 2014.

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The depletion of ozone over the Antarctic stratosphere, particularly in the beginning of springtime, has been the subject of a great deal of attention during the last decade. This phenomenon has been also recently observed in the Arctic stratosphere especially during the unusually cold 1995-96 winter.

The actual picture, which describes the chemistry involved in the polar stratosphere, takes into account heterogeneous and homogeneous reactions in two steps: 

(i) During the polar night heterogeneous processes on the surface of polar stratospheric clouds (PSCs) convert inactive chlorine in the form of reservoir molecules such as HCl and ClONO2 into active photolizable forms according to the following reactions:

ClONO2 + HCl → Cl2 + HNO3          (1)
ClONO2 + H2O → HOCl + HNO3          (2)
HOCl + HCl → Cl2 + H2O          (3)

(ii) In currently accepted homogenous chemistry, diatomic chlorine released into the atmosphere by steps (1) and (3) is quickly photolyzed into atomic chlorine in early spring. It destroys polar ozone primarily through the ClO dimer catalytic cycle involving the reaction:

Cl + O3 → ClO + O2          (4)

The production and release of molecular chlorine are crucial steps in the ozone-depletion cycle, since Cl2 photolyzes readily in sunlight to provide a steady source of chlorine radicals.

The full article is free to read in Progress in Reaction Kinetics and Mechanism, Volume 26, Numbers 2-3, 2001, pp. 179-199

Follow Progress in Reaction Kinetics on Twitter @ProgRKM

Image: Earth 3D (Clouds & Topography maps come from earthobservatory/nasa), courtesy of vinz89/Shutterstock.com