Overall Situation - In December, the average PM2.5 concentration in 339 cities was 44.6 micrograms per cubic meter, an increase of 3.5% year-on-year [2] - The average PM10 concentration was 71 micrograms per cubic meter, up 7.6% year-on-year [2] - The average O3 concentration was 86 micrograms per cubic meter, an increase of 1.2% year-on-year [2] - The proportion of days with good air quality was 84.8%, down 3.2 percentage points year-on-year [2] - For the entire year, the average PM2.5 concentration was 28.0 micrograms per cubic meter, a decrease of 4.4% year-on-year [2] Key Regions Beijing-Tianjin-Hebei and Surrounding Areas - In December, the average PM2.5 concentration was 63.9 micrograms per cubic meter, an increase of 26.8% year-on-year [4] - The average proportion of good air quality days was 65.6%, down 15.3 percentage points year-on-year [4] - For the entire year, the average PM2.5 concentration was 37.3 micrograms per cubic meter, a decrease of 11.6% year-on-year [4] Yangtze River Delta - In December, the average PM2.5 concentration was 49.1 micrograms per cubic meter, a decrease of 10.1% year-on-year [6] - The average proportion of good air quality days was 81.7%, down 0.6 percentage points year-on-year [6] - For the entire year, the average PM2.5 concentration was 31.7 micrograms per cubic meter, a decrease of 3.9% year-on-year [6] Fenwei Plain - In December, the average PM2.5 concentration was 56.3 micrograms per cubic meter, an increase of 19.8% year-on-year [7] - The average proportion of good air quality days was 75.2%, down 10.9 percentage points year-on-year [7] - For the entire year, the average PM2.5 concentration was 33.7 micrograms per cubic meter, a decrease of 14.9% year-on-year [7]