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Measures to improve Otago's winter air pollution to set standards have failed in all but two of the region's towns, triggering a review of the Otago Regional Council's management of the problem.
The council is to review its air quality management strategy after monitoring last winter confirmed many towns in the region would not meet the National Environmental Standard for Air Quality (NESAQ).
Under the standard, towns are allowed to exceed the daily standard - of 50mcg per cu m of airborne pollutant, with a particle size below 10 microns - only three days a year by 2016 and then one day a year by 2020.
Alexandra breached the standard 47 times last winter, Milton 42 (once as high as 139mcg) and Cromwell 33.
The council's own daily standard of 50mcg, exceeded only once a year - set in the Regional Plan: Air in 2006 - was to be complied with by last September but only central Dunedin and Palmerston met the target.
Council air quality scientist Deborah Mills said, in a report to be considered at tomorrow's technical committee meeting, several initiatives had been undertaken to achieve compliance but analysis of the monitoring results showed progress had been uneven.
''There are numerous challenges to meeting the NESAQ in Otago. These cut across social, economic, cultural, logistical, technological and the greatest climatological issues.''
There had been some improvements, she said. Last year, Arrowtown had its lowest winter average, 30 micrograms per cu m of air, since records began in 2006; Clyde's maximum PM10 levels (very small particles) had decreased by 30% and Mosgiel's 10 highest days dropped 15% on the long-term average.
''However, it is unlikely that Alexandra and Arrowtown will meet the NESAQ.''
Those two towns, along with Milton, experienced some of the worst air quality in the country and represented about 7% of Otago's population, she said.
About 20% of those households had taken part in the council's Clean Heat, Clean Air compliant heating scheme, resulting in an estimated 10%-20% reduction in emissions.
The towns were also climatically challenged, in terms of air quality, as they were situated at the base of hills or dams and, in very cold and still winter conditions, there was little air movement for smoke dispersion.
Preliminary work on new projections indicated that even if the rate of change was able to be sustained in Alexandranational air quality standards would not be achieved by 2020.
''Sustaining the current rate of change is unlikely, as well, given that the central government subsidy for domestic heating appliances has ended.''
Other challenges included finding quality alternative heating, the cheapness of coal, relative to the increasing costs of electric or gas heating, and the logistics of being able to source or store dry wood.
Despite this, a large majority of people in Otago lived in towns with relatively good air quality, she said.
Dunedin had experienced its best air quality year since 2006. It has met national guidelines two years in a row.
Mosgiel had only a ''handful'' of high-pollution days this year.
It took five consecutive years of meeting the guidelines for a town to be considered not polluted.