Hanoi becomes most polluted city, as thick smog engulfs Vietnamese capitalbr br Vietnam’s capital Hanoi takes the top spot for air pollution among global cities on Feb. 12, 2025, as reported by iQair, a leading air quality monitoring service that tracks and rates pollution levels using the Air Quality Index (AQI). With a population of nearly 9 million and over 8 million registered motor vehicles, Hanoi faces significant air pollution challenges, which are exacerbated by the burning of agricultural and household waste, as well as emissions from industrial and construction activities, highlighting the need for a comprehensive approach to address the city's environmental concerns.