The study also showed South Asia's fight with worsening air quality and the economic toll it is expected to take worldwide.
Seven Indian cities that rank in the top 10 list of most polluted cities in the world includes Ghaziabad, Faridabad, Bhiwadi, Noida, Patna, Lucknow and Delhi. India notches up health-care costs & productivity losses from contamination of as much as 8.5 % of GDP, according to the World Bank.
PM2.5, or particles of 2.5 micrometers or less in diameter, is so risky because it lodges deep in the lungs.
Seven of the world's 10 most polluted cities are in India.
Delhi had an average yearly PM2.5 concentration at 113.5 micrograms per cubic metre, followed by Dhaka at 97.1 micrograms per cubic metre. Air pollution is likely to cause the death of almost seven million people around the world in the next year and will cost around $225 billion to the global economy, he added.
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The index measures the presence of PM 2.5 which is a pollutant which can go deep in the lungs and bloodstream of a human being causing various respiratory and other lung diseases.
The report is based on 2018 air quality data from public monitoring sources, such as government monitoring networks, supplemented with validated data from outdoor IQAir AirVisual monitors operated by private individuals and organisations.
The report accompanies an extended online interactive display of the world's most polluted cities, allowing further exploration of air quality across different regions and sub-regions in 2018, it said. In addition to human lives lost, there's an estimated global cost of $225 billion in lost labour, and trillions in medical costs.