Four years of air-quality testing in Otago have failed to detect any trends, but have confirmed Alexandra, Arrowtown and, more recently, Milton have the worst air quality during winter.
The data, from 14 sites, was collected for the State of the Environment report on air quality in Otago between 2005 and 2008, which was an interim report on the progress being made towards compliance with the National Environmental Standards (NES) by 2013.
NES requires that the average daily PM10 (very small particulates) level not exceed 50mcg per cubic metre in a 24-hour period more than once a year. It also requires a steady improvement in air quality from 2005.
To help meet the standard, the council's Air Plan set a daily goal for PM10 of 35mcg a cubic metre.
Council air-quality scientist Deborah Mills said in a report to the environmental science committee Otago residents enjoyed very good air quality for much of the year..
Poor air quality was experienced more than 30 times a year in Alexandra, Arrowtown, Clyde, Cromwell and Milton. Dunedin, Mosgiel and Oamaru only occasionally experienced it.
"To meet the 2013 AQNES timeframe, considerable cleaning up of the winter air is required in these towns," she said.
The difference in air quality in Otago towns was due to several factors, including differing numbers of solid fuel burners and type of fuel burnt, and variations in climate and topography.
A summary of statistics of PM10 monitoring showed Alexandra had the highest annual average of 26mcg, the highest May to August average of 49mcg and the greatest number of days (48) a year over 50mcg.
The highest one-day PM10 value was experienced in Arrowtown (168). Milton, which has only been monitored for one season, had the greatest percentage of days over the Otago goal level of 35mcg (35) and the second highest number of days a year over 50mcg (46).
Results also showed PM10 levels could exceed 100mcg in Clyde and Cromwell during winter.
However, in Central Dunedin, higher levels of PM10 were experienced in spring, summer and autumn, than in winter.
With the exception of North Dunedin, which had shown a marked decrease in PM10 levels over several years, it was not possible to identify significant trends in air quality, she said.
Environmental information and science director John Threlfall said the report held no great surprises and it was too early to tell whether the council's air-quality mitigation measures were making a difference.
Cr Duncan Butcher said the council was embarking on expensive projects on the assumption it would help the air quality situation, so some sort of reporting linking the impacts of the two was needed.
