so did they?

hourly CN air quality map, unit is µg/m³: https://www.air-level.com/

reuters says “The WHO considers PM2.5 concentrations above 50 micrograms per cubic metre “severe” air pollution.” but I couldn’t actually find that in WHO global air quality guidelines or anywhere else. china considers >500 µg/m³ “severe” (严重) and everything on the map would be below that