SCIENTIC STUDY OF STRATOSPHERIC AIR CIRCULATION SUGGESTS AN EARLIER OZONE LAYER RECOVERY

CFCs are generally very stable in the troposphere (low atmosphere) and degrade to release ozone destroying chlorine only in the stratosphere. Such Ozone Depleting Substance (ODS) are carried to the stratosphere by natural air circulation and so the rate of addition of chlorine to the stratosphere is  linked to the rate of exchange of air between troposphere and stratosphere and the length of time it remains there.

In the Scientific Assessment of Ozone Depletion in 2006 and subsequent Assessments, this "residence time" was estimated to be around 8 years for transport between the lower atmosphere and the Antarctic pole.

A recent scientific paper has however shown that the residence time of air – and of the ODS it contains, is much shorter than current models, since 75% of it will have returned to the troposphere within only 3 years only (figure 1).

This much shorter residence time can have important consequences for the recovery of the ozone layer (figure 2 from the ODGI page).

Firstly, with a faster decay rate, the EESC slope in figure 2 would be steeper.

Secondly, moving the curve to earlier years, because the stratospheric circulation is faster, as suggested in the paper, will give a higher 1980 value (reference year when there was no unacceptable ozone depletion).

Consequently the return to pre-ODS levels would be speeded up both by the faster stratospheric circulation and because of the higher target level.