Vietnamese capital Hanoi was blanketed by a thick haze of pollution on Tuesday that obscured high-rise buildings and left the city’s nearly nine million people breathing toxic air.
The city topped air monitoring website IQAir’s table of the world’s most polluted cities early Tuesday afternoon.
Levels of PM2.5 pollutants—cancer-causing microparticles small enough to enter the bloodstream through the lungs—were classified as “very unhealthy” and hit more than 24 times the World Health Organization’s annual guideline.
In recent years Hanoi has frequently been listed among the world’s most polluted cities, due in part to widespread construction and emissions from the huge number of motorbikes and cars that crisscross the capital every day.
The latest World Bank report on air pollution says 40 percent of people in Hanoi are exposed to concentrations nearly five times greater than WHO guidelines.
The WHO says that a number of serious health conditions are linked to air pollution exposure, including strokes, heart disease and lung cancer.