In Shanghai (at least, Pudong and Puxi), mask usage has jumped dramatically since last week. I haven't actually kept score, but my impressions of usage from walking around a lot are:

- Summer/spring (lower pollution — Chinese AQI around 60–100, with spikes to 150): 5-10% of people wear masks outdoors. The indoor rate is lower (2-3%?).

- December/early January (AQI typically above 120): 20-30% outdoors. The indoor rate is much lower.

- As of January 23/24: 80-90% outdoors. The indoor rate is at least as high. This time period includes a couple of anomalously low-pollution days (AQI 30 — the lowest I've ever seen in Shanghai), when I might otherwise expect mask usage to be even lower than that 20–30% from before the Wuhan events escalated.

This is just people walking around and shopping. As of a few days ago, some businesses, such as Starbucks and Didi (Chinese Uber/Lyft), require employees to wear respirators (and they've messaged to customers on WeChat and in the Chinese Starbucks and Didi apps).