to over 9000' and although mid summer we soon after noticed what appeared to be either a light coating of dust - or otherwise the initial stages of icing beginning to form on the wing surfaces of our Cessna 172J. Any clues as to which it could have been ?
Pasir
You should keep an eye on the temp guage? were you in cloud during the climb or clear air? Midsummer in that region its unusual to get the freezing level at 8-9 K usually higher.
Dust wont stick in the air only as a coating on the ground.
Was it still there when you landed? Again if it was frozen water it would have melted midsummer in the south of France on your way down.
Pace