India capital is worldâ€™s dirtiest city - World - nation.co.ke NEW DELHI, Thursday New Delhi is the dirtiest city worldwide, a World Health Organisation report has revealed. A study of 1,600 cities across 91 countries released by WHO showed 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. This was almost three times as high as the reading for Beijing of 56 despite the Chinese capitalâ€™s reputation for smog, and 10 times that of London. But India denied the reports and accused WHO of bias. â€œWe have data for New Delhi which is not biased,â€ Gufran Beig from the state-run System of Air Quality Weather Forecasting and Research (SAFAR) told AFP. â€œIt takes into account the data taken from 10 air quality monitoring stations spread around the capital in an unbiased way. It is not misleading,â€ Beig said. MONITORING STATIONS The WHO used data for New Delhi from 2010 to 2013 from five monitoring stations in residential and other areas. The data from China, where authorities are under pressure to be more transparent about pollution, was from 2010, the last year for which figures were available. â€œWe are now studying the data for 2011-14 which we have procured from the US embassy in Beijing. This will help us arrive at a more accurate comparison,â€ Beig said. The WHO stressed that its new air pollution database, which relies mainly on data gathered by the cities themselves, did not aim to rank cities.â€ PM2.5 particles are very small in size and can easily enter the body and interfere with the functioning of the lungs. They are also associated with increased rates of chronic bronchitis, lung cancer and heart disease.