WHO's terms Delhi as most polluted city in a select manner:

Government today said the World Health Organisation's (WHO) recent report describing Delhi as the most polluted city of the world by considering estimated data for fine dust in a select manner was "improper".
On the other hand, Environment Minister Prakash Javadekar said, the ambient air quality, which is regularly monitored in NCR, show that although the levels of Sulphur Dioxide (annual average) are within norms in the region, levels of PM10 exceed the limits in NCR while the levels of nitrogen dioxide are exeeding the norms in Delhi.
"The World Health Organisation has recently released Ambient Air Pollution database update 2014 considering only two pollutants - PM 10 and PM2.5 for 1628 cities at global level...

"Whereas National Ambient Air Quality Standards (NAAQS) 2009 notified by the government comprised of twelve pollutants including PM10 and PM2.5...
"The WHO report decribes Delhi as the most polluted city of the world while considering estimated data for fine dust (PM 2.5) in a select manner, which is improper," Javadekar said in a written reply in the Rajya Sabha.
PM10 is the particular matter having the size equal to or less than 10 micron while PM 2.5 is particulate matter having the size equal to or less than 2.5 micron.

In reply to another question, he said while the WHO has ranked cities in the world while estimating the levels of fine dust in ambient air of various cities, a report of Yale and Columbia university has considered on PM 2.5 as the pollutant relying on satellite data in place of actual monitored data, though the data is available.

"NAAQS notified by government envisages 12 pollutants whereas both the reports have relied on eiher one or two pollutants," Javadekar said.
A report on Environment Performance Index (EPI) 2014 has been produced jointly by a team of experts from Yale and Comubia University recently. The report which has ranked 178 countries on 20 indicators has ranked India's EPI at 155.