Experts say pollution in Hanoi is a result of widespread construction, as well as emissions from the huge number of motorbikes and cars that crisscross the capital every day
Thick smog blanketed Hanoi on Friday, obscuring buildings and leaving nine million residents choking on toxic air as the Vietnamese capital topped a list of the world's most polluted major cities.
Authorities urged people to wear masks and limit time outdoors, but commuters told AFP they were struggling to breathe through the putrid smog, now a fixture of the winter months in the city.