As India's north continues to struggle with extreme pollution levels , the story has put a fresh spotlight on air quality in cities across Asia.Delhi's toxic air is particularly dangerous to childrenBeijing has long been notorious for its smog - but statistics show that India, Pakistan and Bangladesh have worse air by far.So why is South Asia so much more polluted?Asia's most polluted citiesOf the world's most polluted 30 cities, 22 are in India , according to research by IQ AirVisual, a Swiss-based group that gathers air-quality data globally, and Greenpeace.The remaining eight cities are all in Pakistan, Bangladesh and China - but the list doesn't include Beijing, which comes in at number 122.Just looking at global capitals, it's also Asian cities that top the ranking .Looking at overall countries, it's Bangladesh that has the worst air, followed by Pakistan and then India.All t
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