Air pollution levels in Dunedin spiked with hourly recordings reaching a high of 205mcg per cubic metre of air on April 11.
The series of high PM10 (very small particulate) readings were recorded between April 11 and 13 and also spiked again on the 19th, a report to be presented to the Otago Regional Council's natural resources committee tomorrow says.
Daily values were 70, 69, 61 and 51mcg per cubic metre of air - above the National Environment Standard of 50mcg per cubic metre of air (50ug/m3) and more than the one "exceedence" allowed a year.
Hourly, the levels regularly reached the 100mcg per cubic metre of air range - including a high of 205mcg per cubic metre of air.
Weather conditions during those first three days were "extremely settled", with very light winds from the eastern sectors and no rain.
There could be several reasons for the spike in air pollution, the report said.
Under calm conditions Dunedin might have been experiencing a pressure inversion due to the ridge of high pressure over the area which would have allowed particulates to stagnate near the surface.
Adjacent road works for the State Highway 88 realignment would also be contributing to the existing PM10 load with fine construction dust, particularly when dispersed by passing vehicles present.
The PM10 levels dropped on April 14 staying below the standard until April 19 when levels spiked again.
