An investigation into Dunedin's air quality has shown there is considerable variation across the city, but what is causing the central city's air pollution problem is not yet known.
The central city's air quality is measured by an Otago Regional Council monitor in Albany St, which shows the area fails the National Environmental Standard (NES) for PM10 (small particulates) about six times a year.
Cr Gretchen Robertson said at an environmental science committee last week just what caused the failures - such as industry, home heating or salt spray - had not been pinpointed.
Potentially all those factors contributed, she said.
A further study was planned to see if the causes of the failures could be identified.
Environmental resource scientist Jono Conway said the pattern of PM10 in central Dunedin was very different from any other site in Otago.
While failures of the NES were generally only experienced in winter, at Albany St the summer months exhibited a similar average level of PM10 to the winter months.
The time when PM10 was at its highest was also different from other sites, in that it was at its highest during the day.
This indicated the source was likely to come from multiple sources, not mainly solid fuel domestic heating as with other sites, he said.
The monitoring for the spatial air quality study showed PM10 concentrations varied widely across Dunedin on winter days.
It also showed the Albany St monitor was in the right place.
"You can go over the hill and it'll be quite different."
It was hoped the new study would "lock down the salt issue", as it would measure different sized particles to determine sources such as sea salt, vehicle emissions or wood, he said.
However, just because salt was a natural phenomenon it did not mean it could be disregarded from PM10 measurements.
Chairman Stephen Cairns said it was "farcical" that salt air could be seen as a negative when everyone sought to live and walk by the sea.
"We all accept dust is not good, . . . . [but] salt. What next?"
Resource management director Selva Selvarajah said salt was not a health issue and most failures happened in extremely calm conditions when neither salt nor dust could be blown around.
The aim of the reports was to use the monitoring information smartly to achieve the best outcome for the city, he said. rebecca.fox@odt.co.nz
