Fifteen years ago, Beijing¡¯s Liangma riverbanks would have been smog-choked and deserted in winter, but these days they are dotted with families and exercising pensioners most mornings.

The turnaround is the result of a yearslong campaign that threw China¡¯s state power behind policies like moving factories and electrifying vehicles, to improve some of the world¡¯s worst air quality.

Pollution levels in many Chinese cities still top the World Health Organization¡¯s (WHO) limits, but they have fallen dramatically since the ¡°airpocalypse¡± days of the past.