AQI became part of everyday Chinese vocabulary during the 2013 Beijing 'Airpocalypse,' when readings repeatedly pinned at 500+. It's the standard English acronym used directly in Chinese — everyone from weather apps to grandparents says 'AQI.' The Chinese equivalent
空气质量指数 (kōngqì zhìliàng zhǐshù) is the formal name, but the three-letter shortcut won.
