Air pollutants decreased between 2016 and 2023

Smoke emitting into the sky Photo: RNZ / Cole Eastham-Farrelly

New air quality data released today shows air pollutants have mostly decreased across the country between 2016 and 2023.

However, according to figures released by Stats NZ, the South Waikato town of Tokoroa is still one of the worst in the country when it comes to hazardous particles in the air.

PM10 and PM2.5 are particles that can be suspended in the air and are less than 10 micrometres and 2.5 micrometres in diameter, respectively.

"PM10 can be breathed into lungs and PM2.5 is small enough to enter the blood stream. Concentrations of particles, gas, and liquid in air can be harmful to human health and contribute to health issues such as cardiovascular and respiratory health problems and increased mortality," said Stats NZ environment and agricultural statistics senior manager Stuart Jones.

The Tokoroa monitoring site, along with Reefton Area School and and Timaru's Anzac Square had the highest average number of days at 100 percent or more of the guideline per year of PM2.5.

The Tokoroa site was also in the top three for highest average daily exceedences of the PM10 standard per year, along with a site in Timaru, and another in Arrowtown.

Waikato Regional Council senior scientist Jonathan Caldwell said Tokoroa's air was polluted because of a mix of social and environmental reasons.

"We do tend to see, in some of our lower socio-economic areas, people tend to rely on burning wood - especially in Tokoroa where there might be easier access to free or cheaper woods," he said.

This wood may not be properly seasoned and if wood is quite wet it puts off a lot more particles which pollute the air.

"Also, if your home is not properly insulated, and that's what we might typically see in some of these lower socio-economic areas, their homes will be harder to heat so they may have to burn more fuel to heat the home that's not properly insulated."

Added to that is the fact that Tokoroa is well inland and gets less wind in winter to blow the pollutants away.

"So, you tend to get inversion layers during the winter where that colder air is trapped below a warmer air above that... they can't disperse because wind speeds are very low and so you tend to get those air pollutants accumulating, especially overnight," said Caldwell.

Other similar-sized New Zealand towns close to a coastal area might have the same number of pollutants but they would be more likely to blow away.

Waikato Regional Council did used to fund clean-heat replacements, subsidising new, more efficient, wood burners or heat pumps. This fund was cut in the latest regional long-term plan.

The local South Waikato District Council could introduce a bylaw to progressively outlaw old wood burners. Rotorua Lakes Council introduced such a bylaw and has had a great improvement with its air quality.

"Rotorua had similar air pollutant problems, or air quality as Tokoroa... and what we've seen over that same period of time, since that bylaw has been introduced, is very large improvements in air quality so the number of exceedances has dropped to pretty much almost zero now," Caldwell said.

Caldwell said it was important for people to know that any amount of breathing in particles would affect health, especially if they were vulnerable. He suggested people seek to understand the impact they might be having on their neighbours.

"So if you are you have a wood burner and you haven't really thought too much about how much smoke you're producing it's probably a good idea to - when you light the fire - to go out and go 'oh, looks quite smoky, maybe I need to do something'."

If the air was looking very polluted or smoky, Caldwell also suggested avoiding any vigorous outdoor activity.

"It's not a good idea to perhaps go running when you've got a high pollution levels, because you're taking in more air from your lungs so you're filtering more about particulate through your lungs," he said.