Vietnam’s capital has been blanketed in toxic air for weeks with one index briefly making Hanoi the world’s most-polluted city on Friday, putting pressure on authorities to take tougher action to tackle the smog.

Thick smog causes air quality levels in to hit hazardous levels:: Hanoi, Vietnam:::: Nguyen Ninh Huong, Student“In the early morning, I thought it was fog on the way to take my exam, but I later found out that it was actually fine dust that reduces my vision and makes me feel like it is not healthy to breathe.

The Vietnamese capital Hanoi topped the list of the world’s most polluted city on Friday, according to daily weather data. Data from AirVisual, an independent provider of global air pollution figures,