Brilliant input thanks Scott and you jolted my memory into something he said.
Nitrogen Oxide emissions from jet aircraft create ozone in the troposphere,
He mentioned the global results showed this huge trend which was
repairing the Ozone layer in the Southern Hemisphere especially, (along with changes of spray can repellents etc) but there was still a huge hole reaching up over NZ, though reducing. (sic).
P.S. No CONTRAIL CONSPIRACY floggas here please!