I lived in Taipei in the 1990s and have been back many times since. Prior to 2002, I rarely would see people wearing them while riding scooters, but never anywh

I lived in Taipei in the 1990s and have been back many times since. Prior to 2002, I rarely would see people wearing them while riding scooters, but never anywhere else. After the shock of SARS, that changed - people starting wearing them on subways, airplanes, on the street, etc. It was a major urban public health panic, and the building quarantines, airport health checks, and media coverage freaked people out. 15+ years later, it's not pervasive. Last summer when I went back I spotted a few people on the subway and airplanes wearing them, and it's pretty widespread among scooter riders, reflecting (I think) a sensitivity about air quality along with a mild concern about catching something from the people around you.