Another cold, settled, frosty night in Hastings may have pushed air-quality standards to the limits again this week, possibly resulting in another exceedance, which would be the third for the year.

Although the 24-hour average figures were not yet in by lunchtime yesterday, from 8pm on Tuesday through to the early hours of yesterday the monitoring site at St Johns in Hastings recorded some high hourly peaks of harmful particles in the air, said Hawke's Bay Regional Council air-quality scientist Dr Kathleen Kozyniak.

"At about midnight it was up to 180 micrograms of PM10 [very small particles] per cubic metre of air, and at 1am it was at 150.

"With those kind of figures we could be looking at another exceedance," Kozyniak said.

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The limit for PM10 concentrations was 50 micrograms per cubic metre of air, and this reached an average of 52 micrograms for the 24-hour period to midnight on Friday last week.

It followed an earlier exceedance at both Hastings and Napier with an average 24-hour level of 55 micrograms PM10 per cubic metre of air in the middle of June.

Before that reading, Napier had not breached the air quality standards for four years, and Hastings has reduced air pollution substantially in recent years, having only one exceedance last winter (compared with seven in 2016).

Like last weekend, the settled, frosty conditions, combined with people using their wood burners, was likely to be behind yesterday's high levels, Kozyniak said.

The PM10 in smoke was a health issue both inside and outside homes, especially for people with respiratory problems.

"There's no known safe level of PM10 and we are looking for continuous improvement, which has happened since 2008."

At that time she said 24-hour average exceedances were more in the region of 70 to 80 PM10 per cubic metre of air.

"We're now within five points of the standards so we do not have far to go - but we can't be sure what's causing these recent exceedances - it could be that with it being so wet this winter people are burning wet wood."

She said generally, with a good fire and dry wood, the heat being emitted should be more of a clear haze than thick smoke.

As such the advice to people was to source and use dry wood whenever possible and to use other means of heating alongside fires.

Being closer to the sea, Napier tended not to have the problems Hastings did, with slightly higher temperatures and sea breezes.

Orchard burnoffs were also an issue, despite there being rules and regulations around such activities, prompting Hawke's Bay Regional Council chairman Rex Graham to advocate for even stronger regulation in June last year.

At the time, he said there were alternative options to burn-offs, although there would be a sizeable cost difference between them - ''but cost is not a justification for pollution''.

At present no consent is needed to burn vegetation and untreated wood outside except during winter from May to August, on properties within the Napier or Hastings airsheds.

If any burning breaches air-quality rules, the council can take enforcement action.

Kozyniak said there was a concern in the community about orchard fires and smoke.

"We advise people to ring the pollution hotline if they see anything that they think needs checking."

On the whole, however, with the hourly peaks of air pollution seen in the middle of the night, woodburners were still considered the main contributors when air-quality standards were exceeded, she said.