Long term trends show Otago air quality is improving, but more work is needed

A report presented at the Otago Regional Council’s (ORC) Data and Information Committee today shows air quality has improved over the last ten years, although the amount of particulate matter in the air in seven out of eight monitoring areas still exceeds the National Environmental Standards for Air Quality.

The Otago Regional Council (ORC) today received a report on the states and trends of air quality in Otago between 2010 and 2019.

ORC monitors air quality at seven State of the Environment monitoring sites around the region. The primary air quality parameter measured at these sites is PM10, which stands for particulate matter smaller than 10 micrometres.

PM10 from human activity is produced by combustion sources such as industrial activity, vehicle exhaust and solid fuel burning for home heating. It can also be produced by vehicle movements or processes that create dust. The majority of PM10 emissions in most parts of Otago come from home heating.

General Manager Strategy, Policy and Science Gwyneth Elsum said the report showed air quality was gradually improving at the majority of sites.

“Winter air quality trend analysis showed improvements in Alexandra, Arrowtown, Clyde, Cromwell and Milton over the ten-year period. These towns have the strictest Air Plan rules for wood burner emission rates and thermal efficiency, and are the areas where ORC has previously incentivised residents to replace older burners.

“Air quality in Mosgiel and Central Dunedin was also trending in a positive direction, and the air quality trends in all towns are more statistically significant than the last time a long-term analysis was undertaken, in 2016.”

Balclutha, where monitoring ceased in 2018, was the only site where the air quality trend was degrading over the long-term.

Despite the overall trend of improvement, seven out of eight sites are still non-compliant with the National Environmental Standards for Air Quality, which limit the average concentration of particulate matter over a 24-hour period to 50 µg/m³, or 50 micrograms per cubic metre. A site is non-compliant if it exceeds this limit once in a year.

The compliant site is Central Dunedin, which has different typical emission sources, meteorology, and climate from the other sites.

Ms Elsum said that the air quality picture is complicated in areas that are experiencing rapid urban growth.

“Different towns in Otago have different climates, geography, and changing population sizes, and these local factors all contribute to air quality. We also know that air quality can change spatially within towns, sometimes quite dramatically.”

The data in the States and Trends report will inform policy making in the upcoming Air Plan review, Ms Elsum said.

“Our Long-term Plan includes a review of the current Regional Plan: Air for Otago starting in the next financial year, before notification in 2025 and implementation in the years after. This state of the environment report will be a key data set for the Air Plan review, and it has also highlighted a few knowledge gaps that we are working to fill with an upgrade to our monitoring network.”

ORC’s Long-term Plan 2021-31 includes funding of $1m in Year 4, $2m in Year 5, and $3.5m per annum from Year 6 on (plus inflation) for measures to support the new Air Plan.

Anyone in the community will be able to have their say on air quality issues and rule changes when the Air Plan review is open for consultation in the 2022-23 financial year.

ORC monitors air quality at seven sites around Otago: Alexandra, Arrowtown, Central Dunedin, Clyde, Cromwell, Milton, and Mosgiel. Air quality data for Otago can be accessed online through Land Air Water Aotearoa (LAWA), at www.lawa.org.nz/explore-data/air-quality/.

The full report, State and Trends of Air Quality in the Otago Region 2010 – 2019, can be viewed in the Data and Information Committee agenda: https://www.orc.govt.nz/news-and-events/events/2021/september/data-and-information-committee-8-september.

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