LATEST: A United Nations agency has today suddenly withdrawn data which yesterday was showing Auckland with New Zealand's worst air pollution at levels nearly double that of Sydney.

New data that is to go on the World Health Organisation (WHO) air pollution survey will show Auckland only slightly worse than Sydney, and Dunedin, which yesterday had the country's cleanest air, now has the worst.

Yesterday's figures showed New Zealand's cities had higher than acceptable levels of air pollution caused an uproar and saw Environment Minister Nick Smith contacting WHO for clarification as the results were out of line with government data.

"The figures released by the World Health Organisation differ from the data collected through monitoring of air quality by New Zealand's regional councils compiled by the Ministry for the Environment.

"Environment Ministry officials have contacted WHO to clarify how it calculated its figures and are awaiting a response," Smith said.

This morning the results for New Zealand had been changed on the WHO website.

WHO's original figures were based on 2009 data but new 2010 official New Zealand data paints a different story - although with no explanation over why they are so different.

WHO published air quality data for 1100 cities across 91 countries, focussing on an air pollution measurement known as PM10, a level of airborne particles smaller than 10 micrometres.

WHO air quality guidelines for PM10 is 20 micrograms per cubic metre (µg/m3) as an annual average.

New Ministry of Environment data is being entered on the WHO site.

Dunedin scored worst in the latest figures with 25 µg/m3.

Yesterday it was just 19 µg/m3.

Auckland is now at 15 µg/m3 against yesterday's 23 µg/m3.

Wellington is now 13 µg/m3 against yesterday's 21 µg/m3.

Christchurch now has New Zealand's cleanest air on 11 µg/m3.

Yesterday it was scoring 20 µg/m3.

Hamilton today scores 13 µg/m3, an improvement on yesterday's 22 µg/m3.

New Zealand's annual mean score is now 14 µg/m3 when yesterday WHO was saying it was 22 µg/m3.

It is not obvious on the WHO spread sheets where other nations have challenged the data.

Based on WHO's data yesterday Australia overall scored 13 µg/m3 with Brisbane top on 18, Port Phillip (Melbourne) 13, Sydney 12 and Canberra 10.

The cleanest urban air in the world was in Yukon's provincial capital Whitehorse, Canada, on 3, followed by Kitimat on 4.

The most polluted city in the world was Ahwaz, Iran, on 372, followed by Ulaanbaatar in Mongolia on 279 and Delhi, India, 198.

WHO says outdoor air pollution causes an estimated 1.34 million premature deaths a year.

Investments to lower pollution levels quickly pay off owing to lower disease rates and, therefore, lower healthcare costs, it said.

In its study, WHO says persistently elevated levels of fine particle pollution are common across many urban areas.

Fine particle pollution often originates from combustion sources such as power plants and motor vehicles.

"Air pollution is a major environmental health issue and it is vital that we increase efforts to reduce the health burden it creates," said Dr Maria Neira, WHO Director for Public Health and Environment.

"If we monitor and manage the environment properly we can significantly reduce the number of people suffering from respiratory and heart disease, and lung cancer.

Across the world, city air is often thick with exhaust fumes, factory smoke or soot from coal burning power plants.

In many countries there are no air quality regulations and, where they do exist, national standards and their enforcement vary markedly.

- © Fairfax NZ News

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