With the onset of winter Masterton residents will be lighting fires, and unintentionally polluting the air around them.

Air pollution is an issue for the town, the environmental standard for particulate PM10 - a small particle that can harm the lungs - being breached on 13 days last winter.

An even smaller particle, PM2.5, exceeded standards on 34 days.

Greater Wellington Regional Council team leader air and climate, Tamsin Mitchell, said Masterton's air quality depended on weather and if it was a cold, calm winter, it was worse.

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"You are really at the whim of the weather for high air pollution nights."

She said the town had low wind speeds and cold temperatures overnight which meant air pollution from wood burners was not readily dispersed and could build up to unhealthy levels outdoors.

She said in 2013 there were 14 breaches and last year 13 breaches.

"It's not clear what the trends are but it doesn't appear to be getting any worse."

A special offer for Masterton residents to replace old wood burners and open fires with clean heating appliances such as heat pumps, pellet burners or flued gas heaters started in March.

Ms Mitchell said the number of people using solid fuels in fires had stayed roughly the same since 2006. "People are sticking with that method, according to the Census."

So far 17 people had taken up the offer, allowing them to borrow up to $5000 against their future rates bill and repay it back over nine years.

"We are hopeful air quality will get better as people move to the new, more modern wood burners."

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Masterton District Council spokesman Sam Rossiter-Stead said the council was doing everything it could and the scheme would help people get the right type of appliance. It was also an education process and the council encouraged people to burn wood correctly.

Ms Mitchell said the council also had a project under way to look at climate influences on year-to-year variability in air pollution levels in Masterton.

For information about the offer, call 0800 496 734.