Air quality reports for various areas throughout Otago were presented to the Otago Regional Council last month.
The annual air quality report 2023 outlined monitoring efforts over the year and compared data gathered against the current national environmental standards for air quality (NESAQ) limit.
"One of the biggest improvements is the reducing number of air quality exceedances in Arrowtown over the past six years", council air scientist Sarah Harrison said.
"These have continued to decrease with just 10 exceedances last year, compared to almost 30 recorded in 2018 — although there is still plenty of room for improvement."
The NESAQ allows for only one exceedance per year per airshed.
The annual report also noted improvements being made to the State of the Environment monitoring network to include monitoring for PM2.5 particles which are smaller and therefore can be harmful to health.
Upon validating last year’s winter data, Otago recorded only 17 exceedances of the NESAQ for PM10 — particulate matter with a diameter of less than 10 micrometres — during the winter of 2023.
Otago has several towns where air quality is considered degraded during winter — Alexandra, Arrowtown, Clyde, Cromwell, and Milton.
In Otago, the main source of particulate matter is home heating emissions in winter.
Long-term exposure to PM10 and PM2.5 contribute to the risks of cardiovascular and respiratory conditions.
Recent research provided evidence that air pollution was dangerous at lower concentrations than previously thought and supports the lowering of existing guidelines.
Continuous monitoring of PM10 was carried out in the Alexandra, Arrowtown, Central Dunedin and Mosgiel airsheds during 2023.
Significant reductions in emissions are required to meet the NESAQ for PM10 in many Otago towns.
All sites except for central Dunedin recorded exceedances of the NESAQ during the winter; the limit for 24-hour PM10 is 50 micrograms per cubic metre of air.
PM2.5 was monitored in Arrowtown, Central Dunedin, Clyde, Cromwell, Milton and Wānaka.
Arrowtown, followed by Milton, had the highest annual and winter average concentrations for PM2.5.
The council conducted a trial study in Arrowtown monitoring black carbon from March to October last year.
Data collected showed a strong seasonal pattern, with higher concentrations during winter, similar to that of PM10 in Arrowtown, but on a much smaller scale.
The periods when black carbon was highest was between 8am and 9am and between 7pm and 9pm, which is similar to home heating patterns found in PM10 monitoring.
"These results are to be expected as they have the same source — home heating emissions", Ms Harrison said.
Black carbon comes from incomplete combustion.
The size, shape and composition of black carbon particles can change as they age and react to other chemicals in the atmosphere.
New Zealand research shows that black carbon concentrations are likely to be highest in areas of high traffic and/or high use of solid-fuel burning for home heating.
Niwa conducted a spatial study in Alexandra using 42 temporary sensors to understand more about the variation in PM concentrations there.
Peak average concentrations were in the northwest. These concentrations are about double the concentrations in other parts of Alexandra and quite far from the monitoring site.
— Staff reporter
