THE extended shut down of the Incitec Pivot acid plant has resulted in increased sulphur dioxide emissions from Xstrata's copper smelter.
Since 2000, the acid plant has taken the bulk of the copper smelter's emissions to create sulphuric acid used to make fertiliser, about 80 per cent.
An Xstrata Mount Isa Mines spokeswoman said all emissions were currently being released through the stack.
"During the shut down maintenance period of Incitec Pivot Limited, 100 per cent of our sulphur dioxide is sent through to our copper stack," she said.
She said the increased emissions would not reach harmful levels.
"During the shutdown of the acid plant, Xstrata Mount Isa Mines will continue to operate its smelters in accordance with procedures undertaken by its air quality control system, which is the most intensive air quality monitoring system of any city in Australia," she said.
"The air quality control system in Mount Isa directs the smelters to shut down if unfavourable wind conditions blow smelter emissions eastwards towards town and they impact the local community."
Incitec Pivot had to extend the routine maintanence shut down of its acid plant when workers discovered extra work needed to be done.
The acid plant is expected to be back online by mid to late March.
Incitec Pivot has estimated the shutdown will reduce its annual profit by $21 million.