Fig. 1.
Variations in air quality and the associated meteorological condition index over China and key regions from 2015 to 2022. a, Annual average PM2.5 concentration. b, Annual average EMI. c, Annual 90th percentile of MDA8 O3. d, Meteorological condition index of O3 pollution. WHO AQG: World Health Organization's Air quality guidelines. EMI: Evaluation on meteorological condition index of PM2.5 pollution. BTHs: Beijing–Tianjin–Hebei and its surrounding regions; FWP: Fen–Wei Plain; YRD: Yangtze River Delta; SCB: Sichuan Basin; PRD: Pearl River Delta. This figure is adapted from Ref. [27, 28].