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The Canterbury Regional Council believes industry is to blame for the high amount of air pollution in a Timaru suburb.
Washdyke - on the northern edge of the town - has recorded 20 high pollution nights so far this year - the maximum high pollution nights it is allowed per year is one.
Residents RNZ spoke to near the industrial area say it often smells bad but they were not aware of the high amount of air pollution.
ECAN Timaru operations manager Judith Earl-Goulet said there were many aspects to the investigation to try and determine what is causing the pollution.
"All of the high pollution days seem to be associated with weekdays and during the day time - so there's a fair likelihood that it's associated with industry and human activity.
"We are still looking at natural causes like sea-salt but that's becoming less likely," she said.
A new mobile monitor will be used around the area to try and pinpoint areas of high pollution.
"When monitoring air quality it tells us what the quality is but not the source so it makes things a bit harder.
"Once we get samples from the mobile monitor we can consolidate that data with data from the fixed monitoring site so we can see under certain wind conditions what part of the area the pollution is coming from," Earl-Gourlet said.
Consents in the area will also be monitored.
"It's like putting a jigsaw puzzle together, we do go and talk to the businesses, we check storm water and air consents."
Earl-Goulet said the council has also hired an independent surveyor to do analysis on wind direction and speed to try and see where the source area is.