Eighteen years ago, when I was living in Yogyakarta and traveling around by motorcycle, masks weren't much of a thing there yet, but Yogya is not a particularly large nor congested city by Asian standards. Whenever I had the distinct misfortune of needing to go to Jakarta, on the other hand, masked motorcyclists and becak drivers were not an unusual sight, due to the truly horrid traffic fumes. Desert sand storms seem to inspire a lot of mask compliance as well, but I'm not sure that they're actually as bad as Jakarta traffic fumes!

— Christophe