With an average air quality index (AQI) of 305, Hà Nội ranked as the most polluted city in the world. HÀ NỘI — According to the IQAir air quality monitoring system, on Friday morning, Hà Nội reached brown levels (hazardous) of 309 and 302 in Tây Hồ District and the downtown area. With an average air... read full story