Dunedin air quality outlier investigated

Air quality measuring equipment next to the University of Otago’s Te Rangi Hiroa residential college in Albany St will be moved this year, the Otago Regional Council says. PHOTO: GERARD O’BRIEN

Dunedin’s reading of 54 micrograms/cu m of particulate matter with a diameter of less than 10micrometres (PM10) in the air on May 27 last year paled in comparison to the 104mcg/cu m that Arrowtown recorded on its worst day of 2021.

Nevertheless, air quality scientist Sarah Harrison said the reading from the central Dunedin monitor

remained under investigation at the council.

In the meantime, the council was moving its air quality monitor in the central city, Ms Harrison said.

Central Dunedin typically had good air quality, and it was uncommon for the site to record PM10 concentrations as high as 54mcg/cu m.

The recording was treated as a significant outlier, she said.

Among the sites the council monitored, only Dunedin had zero days where the air quality breached the standard of 50mcg/cu m, her annual air quality report for 2021 said.

The region’s worst offender Arrowtown hit 104mcg/cu m twice, and the town recorded 22 breaches of the 50mcg/cu m limit last year.

Alexandra hit 62mcg/cu m and had one day over the limit.

Cromwell reached 74mcg/cu m on its way to 11 breaches.

Milton recorded a day of 99mcg/cu m as it recorded nine dirty air days last year.

And Mosgiel recorded a day of 62mcg/cu m and had two breaches reported.

In the air quality report, presented to the council’s data and information committee yesterday, central Dunedin officially recorded a high of 48mcg/cu m, Dunedin’s second highest day was 37mcg/cu m.

Ms Harrison said council staff had considered a range of environmental factors to account for the high reading of 54 mcg/cu m last year.

These factors included a lack of wind and previous rainfall, the main wind directions of pollutants, and the discharge-to-air activities occurring nearby.

The spike in particulate matter in the air that day appeared to be a one-off event, she said.

"At this stage, we do not have a definitive answer to the cause and are continuing to investigate.

"However, our main focus remains on those areas of Otago with long term trends of poor air quality," she said.

Meanwhile, the council would be moving its central Dunedin air quality monitoring site, presently located in Albany St, near the intersection with Anzac Ave, she confirmed.

The air quality monitoring equipment would be relocated a short distance away, near the Clyde St bridge over the Leith, she said.

There were no firm dates for the move, but it was planned for

this year.

As well as dust from construction sites having the potential to impact air quality readings, the present monitoring site would be too close to a new building being built, so was

being moved to a more open area, she said.

Her report also noted the World Health Organisation in September last year updated its guidelines such that clean air standards would drop from 50mcg/cu m to 45mcg/cu m for large particles (PM10) and for smaller particulate matter (PM2.5) the clean air standard was dropped from 25mcg/cu m to 15mcg/cu m.

The council’s monitoring network was presently being upgraded to include monitoring for PM2.5.

hamish.maclean@odt.co.nz