Blenheim has recorded the highest number of exceedances for particulate matter (PM) since air quality monitoring began in 2006, Marlborough District Council has revealed today.
Council’s Environment Committee today received the Annual Air Quality Monitoring Report – Blenheim 2021 which confirmed the town had again failed to comply with the National Environmental Standards (NES) for Air Quality for PM10.
Council’s Environmental Scientist, Sarah Brand told the committee that concentrations of PM10 exceeded the maximum concentration of 50 micrograms per cubic metre (50μg/m3) on 16 occasions in 2021.
“This resulted in 15 breaches of the NESAQ for PM10 whereas the NESAQ allows for one exceedance per year. This is the greatest number of exceedances since continuous monitoring for PM10 commenced in 2006,” said Ms Brand.
The maximum measured concentration during 2021 was 78 µg/m3 which was similar to maximum concentrations measured during 2017 (74 µg/m3) and 2015 (79 µg/m3).
“There were some irregularities in the 2021 exceedances with a greater contribution of coarse particles than usual. A potential source could relate to earthworks associated with the development of land approximately one kilometre from the monitoring site,” she said. “It shows that activities around the region can make a difference.”
In 2005, regional councils were required to outline urban areas which either were, or were likely to exceed, the National Environmental Standards for PM10. These areas were termed airsheds.
In Marlborough, Blenheim is currently the only designated airshed and as such concentrations of PM10 need to be monitored continuously. This is done at the Redwoodtown Bowling Club site, with smaller particulates (PM2.5) also being measured since 2017.
The National Environmental Standards (NES) currently focus on PM10but the Ministry for the Environment is proposing a change to focus on PM2.5 this year.
PM2.5 results for 2021 show that Blenheim exceeded the proposed 24-hour average NESAQ for PM2.5 on 38 occasions which would constitute 35 breaches.
“The proposed NESAQ PM2.5 will only allow for three exceedances per year. Blenheim is therefore unlikely to comply with these guidelines,” said Ms Brand.
An air emission inventory for Blenheim completed in 2017 showed that 90% of the anthropogenic PM10 emissions originate from home heating (mainly wood smoke). Industry, transport, and outdoor burning contribute the remaining 8%. The air emission inventory for Blenheim is due to be undertaken again and completed by the end of June 2022.
“The PM10 standard is usually breached during the winter months when emissions from domestic home heating coincide with particular weather conditions. These include low wind speeds and cold temperatures,” said Ms Brand.
“Management measures to reduce PM10 concentrations to meet the NESAQ have been included in the Marlborough Environmental Plan (MEP) however additional measures are likely to be required to achieve the new standards.”
These could include non-regulatory behavioural change programmes targeting households’ operation of woodburners, ensuring wood was dry and encouraging a shift towards other forms of heating through schemes such as the Council’s Home Clean Heating scheme, Ms Brand said.
Last year Council’s ‘Burning Guides’ had a refresh and an update to increase awareness of these new management measures which are contained in the MEP, she said.
“Burning dry wood is one of the best ways to limit the impacts of particulate matter on air quality. How you operate your wood burner does make a difference to real life emissions,” said Ms Brand.
To view the Council’s Burning Guides, go to: