WHO's air quality guidelines recommended an annual average for PM10 (very small particles) was 20mcg per cu m.
The latest figures showed Dunedin was the only New Zealand city to breach that standard with 25mcg per cu m, while Christchurch recorded 11, Wellington and Hamilton 13 and Auckland 15.
In contrast, Sydney recorded 12, with Brisbane the worst Australian city on 18, and internationally Edinburgh recorded 15, Belfast 18, London 29, New York 21 and Paris 38.
Otago Regional Council director of environmental information and science John Threlfall said he was not convinced the latest figures were correct or if the way cities around the world measured air pollution could be compared.
He also found it hard to believe Dunedin's air pollution was worse than Christchurch's. Its annual average was in the 20mcg-22mcg per cu m range and in winter it went up to 24mcg-27mcg.
Location of air pollution monitors made a big impact on results and in Dunedin the monitor was in the "mixed land use" area of Albany St.
So, although Dunedin did not have a big winter air problem, levels in other seasons were not very low which kept the annual average high, he said.
"The reason behind this include local industry, quarry, traffic including trucks which lift dust, and salt spray."
The 2010 figures in Dunedin were also influenced by the construction of the Forsyth Barr Stadium.
The figures released yesterday differed from those released by WHO just 24 hours earlier, which showed Auckland was the most polluted city.
That data was challenged by Environment Minister Nick Smith, who said figures collected by the Environment Ministry also showed Dunedin to hold the unenviable title.
"When the ministry figures are used, Dunedin is the only New Zealand city to have PM10 annual average levels higher than all of Australia's major cities," Dr Smith said.
"I do find it odd that the WHO figures show Auckland has the worst air pollution in New Zealand when that is contrary to all the historic data which shows our biggest problem is in Christchurch."
Tuesday's figures released by WHO showed Dunedin recorded 20, Christchurch 19, Auckland 23, Hamilton 22 and Wellington 21.
