After ten years in Shanghai, I sometimes forget how rare this level of cleanliness is in a city this size.

I knew what an N95 mask was long before most of my German friends. I breathed Shanghai’s polluted air a decade ago. That has changed—and the world should start paying attention.

In Shanghai, a woman can stroll home at 2 a.m. without a second thought. That is different in Berlin, London, or San Francisco. Here’s Why.