7月，全国339个地级及以上城市平均空气质量优良天数比例为93.0%

Group 1 - The average PM2.5 concentration in 339 cities was 14.5 micrograms per cubic meter in July, showing a year-on-year decrease of 8.2% [1] - The average PM10 concentration was 28 micrograms per cubic meter, down 3.4% year-on-year [1] - The average O3 concentration increased to 138 micrograms per cubic meter, reflecting a year-on-year rise of 4.5% [1] - The average SO2 concentration was 6 micrograms per cubic meter, with a year-on-year decrease of 14.3% [1] - The average NO2 concentration was 11 micrograms per cubic meter, down 8.3% year-on-year [1] - The average CO concentration was 0.6 milligrams per cubic meter, showing a year-on-year decrease of 14.3% [1] - The proportion of days with good air quality was 93.0%, an increase of 1.0 percentage points year-on-year [1] - The proportion of days with heavy pollution was 0.2%, a decrease of 0.1 percentage points year-on-year [1] - The average number of days exceeding standards due to dust storms was 0.6%, with heavy pollution days at 0.2% [1] Group 2 - Among 168 key cities, the top 20 cities with the best air quality included Huangshan, Haikou, and Lishui [2] - The bottom 20 cities with the worst air quality included Yangquan, Jiaozuo, and Luliang [2] - The top 20 cities with the lowest PM2.5 concentrations included Lishui, Zhoushan, and Dazhou [2] - The bottom 20 cities with the highest PM2.5 concentrations included Hebi, Tangshan, and Suizhou [2]