Mumbai: In an indication of the very poor health of the city's air, Mumbai has been declared by the World Health Organisation (WHO) as the fifth most polluted megacity in the world in terms of PM 10 (coarse pollution particles) levels. The city is 39 on the list of most polluted in terms of PM 2.5 (fine, particulate matter) among 122 Indian cities monitored by the WHO. Navi Mumbai and Thane are 36th and 87th. WHO's urban air quality database 2016, released on Thursday , studied pollution in 3,000 cities and towns in 103 countries for 2008-15. Mumbai is 147th on the international scale of all cities (separate from the table on megacities).Gwalior and Allahabad are the second and third-most polluted cities in the world, while Delhi is at 11. WHO used data from government and research organisations. For Mumbai, WHO used the data provided by Maharashtra Pollution Control Board from its monitoring stations in Sion and Bandra. Mumbai recorded an annual average of 117 microgrammes per cubic metre (gm3) for PM 10 which is over five times WHO's safety limit of 20gm3 and almost double the Indian safety limit of 60gm3. This is however better than the 136gm3 recorded in the 2014 WHO report. he concentration of PM 2.5 was 63gm3 which is over six times WHO's safety limit of 10gm3 and one-and-half times more than Indian limits. The levels worsened from 2014 when it was 45g m3. "It is quite apparent. The PM 2.5 levels are high due to the vehicles and construction activity which is high. The other reason is episodic, like burning of biomass or trees," said Rakesh Kumar, director, National Environmental Engineering and Research Institute (NEERI). Both PM 10 and PM 2.5 are classified as carcinogenic by WHO. "Globally , in 2012, air pollution in urban areas is estimated to have caused 3.7 million deaths, more than one-third reported from South-East Asia," said Dr Poonam Khetrapal Singh, WHO regional director for SouthEast Asia.