Hanoi, Vietnam’s capital, has been declared the world’s most polluted city.

• 5 levels reached 266 micrograms per cubic meter.
• Causes include heavy traffic, industrial activities, and trash burning.
• Vietnam is located in Southeast Asia, bordered by China to the north, Laos and Cambodia to the west, and the South China Sea to the east.
• Its capital is Hanoi, and the largest city is Ho Chi Minh City.