The World Health Organisation report that found that the Indian capital city - New Delhi has surpassed Beijing in having the worst air quality has been slammed by Indian researchers as inaccurate.

The WHO report that covers 1,600 cities found air pollution had worsened since 2011, especially in poorer countries, putting city-dwellers at higher risk of cancer, stroke and heart disease.

The report put air pollution as the major hazard that claimed the lives of seven million people in 2012. What was more shame for India was the fact that the WHO report found 13 Indian cities to be the dirtiest ones out of 20 cities around the world.

The dirtiest lot has New Delhi on its top, followed by Patna, Gwalior and Raipur. The WHO report showed that Delhi had an annual average concentration of airborne small particles of less than 2.5 micrometres in diameter, known as PM 2.5, of 153, which is three times as high as the reading for Beijing of 56, despite the Chinese capital's reputation for smog and 10 times that of London.

The Indian environmental agencies, however, have decried the report as biased and misleading. Even the WHO experts insisted that the survey was not intended to name and shame the dirtiest cities, since the cities involved were volunteering to provide information inorder to help themselves clean up. Meanwhile, the Indian officials noted that the WHO report was biased.

"The data is inaccurate and is biased. The average yearly value of PM 2.5 of Delhi ranges between 110-120 microgram/m3, but WHO has overestimated it as 153 microgram/m3 and has underestimated Beijing's average. There is a mismatch in years of comparison. Delhi data of 2013 (traffic signal) is compared with 2010 of Beijing," Dr. Gufran Beig, Chief Project Scientist,  Air Quality Weather Forecasting and Research (SAFAR) told IBTimes.