Hanoi air quality improves, still among Southeast Asia's ...
Photo by Reuters. Hanoi has seen air quality improve over the past year but it remains one of Southeast Asia's most polluted cities. The city's average PM2.5 level last year was 40.8 micrograms per cubic meter of air as opposed to 45.8 in 2017, according to Switzerland-based air quality monitor IQAir AirVisual's 2018 World Air Quality Report.