Are there any issues with blowing on your glasses to clean e.g. dandruff off on shabbos? I was thinking that perhaps it is zoreh/winnowing - similar to blowing dust off old books?
In regards to zoreh applying to blowing dust off old books, I found it in the 39 Melachos book (Rabbi Dovid Ribiat) page 376:
It would also seem probable that the following examples are also forbidden under Zoreh:....Blowing dust off an old book, bookshelf or dusty bottle.
That quote itself is referenced to a footnote - the footnote itself does not cite an exact source for that specific example, but explains why it should apply by citing many similar examples (e.g. where even blowing via mouth and not natural wind is Zoreh), and also gives rishonim sources mentioning that zoreh also applies to dust.