The first cold snaps of autumn have resulted in increasingly high air-pollution levels in some parts of Otago.
Otago's ''hot spots'' for air pollution, Alexandra and Milton, have already exceeded the National Environmental Standard of 50 micrograms per cubic metre of air.
In Milton's case it had done so three times since May 1 with the highest level recorded 75 micrograms per cubic metre of air on May 2, and in Alexandra it had happened twice with the highest 58.7 micrograms per cubic metre of air on May 8.
Otago Regional Council air-quality scientist Deborah Mills said it was not unusual to have high readings in those towns.
The key ingredient to the high readings was overnight temperatures which dropped below freezing.
Often after the initial air-quality spike, as everyone started using their winter heating sources, the pollution levels dropped back, she said.
Arrowtown, another ''hot spot'' for air pollution, had not yet recorded levels over the standard which was encouraging, although it had recorded 46.1 micrograms per cubic metre of air on May 7.
She was pleased to see its levels staying in the low range more often than not.
''We think we are seeing some improvement there as it seems to be getting better.''
The council had put a lot of work into education and its Clean Air, Clean Heat project in the town, she said.
''We'll be watching it closely this winter.''
Balclutha had recorded 35 micrograms per cubic metre of air on May 1 and 2 but had yet to exceed the standard.
Dunedin and Mosgiel, which were in air zone two, had readings in the low range, as did Clyde.
The Otago Daily Times will run weekly air-quality columns from May 18.
