However, the Otago Regional Council says the value of the monitoring it has done over the past seven years in the "most polluted airshed in Otago" should nevertheless be considered.
Commissioned by the council, the Niwa report mapped winter air quality in Alexandra and showed there was a significant variation in air pollution across the town.
The present monitoring site, used by the council since 2017 — although only 720m away from the council’s previous monitoring site — was reporting concentrations of airborne particulate matter 23% lower than the previous site, the report said.
"The current site is fairly representative of median, or average, concentrations across the town, but both the current, and the previous site under-represent the maximum concentrations in the town," it said.
"To comply with current regulatory guidance, we recommend that ORC consider relocating their monitoring station again, closer to the ‘hot-spot’ area identified in this work."
The report said similar monitoring of other towns should be considered.
It also said the council should work with the Ministry for the Environment and other regional councils to promote a review of regulatory guidance and improve air quality reporting nationally.
Council air quality scientist Sarah Harrison said council and Niwa staff had put out 42 low-cost sensors in a grid network across the Alexandra airshed.
The resulting monitoring found the area of the highest concentrations was in the northern end of the airshed.
While "site availability" was quite low in Alexandra, and played a factor in determining the present site, the next step for the project was to monitor both the present site and the previous one for 12 months to establish a relationship between the two.
"We need to figure out, A, if we’re going to move the site and, B, if we’re not, how are we going to reconcile the two sites?"
One of the arguments for not moving the present site was the establishment of long-term trends "and long-term trends are what you want if you want to know whether your policies are working and improving air quality", Ms Harrison said.
"Alexandra is the most polluted airshed in Otago, and probably the country," she said.
"It’s very complex climatically: there’s a lot of converging winds that push the concentrations around, and it leads to quite dramatic spatial variations of pollutants."
Council policy and science general manager Anita Dawe said that with seven years of data it appeared there had been a slight improvement in the town’s air quality.
But it started from a very high base in terms of pollution.
"What we can safely say is things are getting better but we’ve got a long, long way to go," Ms Dawe said.
