China's Provinces air pollution ranking from Jan to Jun 2014: Hebei, Hubei, Henan, Beijing, Shaanxi, Tianjin, Xinjiang & Shandong had more than 50-72% of exceedance days

Bubble pie map of provinces and municipalities over the first six months of 2014 

The 8 following regions and municipalities (see Figures 2 & 3) have had the highest population-weighted average urban air pollution (1^st quintile): Hebei, Hubei, Henan, Beijing, Shaanxi, Tianjin, Xinjiang & Shandong. They concern a population of 139 Mil. 

These regions and municipalities have had 90-149 exceedance days (50-72% of total 181 days) above the threshold of 100 (AQI) and 75 µg/m3 (PM2.5).

The best regions and municipalities (5th quintile) were Hainan, Yunnan, Fujian, Tibet and Guangdong with only 4-18% exceedance days. 

Figure 1 :  Air pollution provinces & municipalities urban air pollution ranking over the first 6 months of 2014 (Jan. to Jun. 2014: 181 days)

The 8 most polluted regions or municipalities are: Hebei (13Mil pop); Hubei (12 mil); Henan (12 Mil), Beijing (19 Mil); Shaanxi (17 Mil); Tianjin (11 Mil); Xinjiang (4 Mil)  & Shandong (50 Mil). AQI is around 120-160 and there are more than 55% of days with AQI>100 (90 on 181  days).

As explained in my post dated 22 Sep 2013, AQI is a random variable with a log normal distribution and the repartition of daily AQI above 50 or 100 AQI is more or less correlated with the average AQI value. 

The correlation is good for days with daily AQI>100,  less good for days with AQI>50 and more loose for days with 50< daily AQI <100.

Figure 2 : Correlation between average AQI and daily AQI repartition