@luciedigitalni @kudra @wscholermann @Seagoon_ The plane trees makes a lot of sense.

Every time I’m in Melbourne, within a couple of days, I get hayfever. Then when I fly up to Sydney, it clears up within a day or two.

I would be seriously surprised if Sydney has significantly less air pollution than Melbourne.

Sydney has the Blue Mountains, the Royal National Park, and Ku-ring-gai Chase surrounding it on three sides.

So just by process of elimination, that leaves the temperature and pollen from some local plant as potential culprits.