Unfortunately I have nothing of substance to add, but I really would like to know the answer to this. So I am subscribing to this thread just to make sure I do not miss the answer.
Also is it only in aluminum you have this gas problem or are there other materials to be careful with too.
If you change to plasma cutting with a bottled gas instead of Compressed air, do you still have this problem?
I know there are some very intelligent folks here who can bread this down for Knut (and Me too)