Professor Simon Hales (left) says much of Christchurch's air pollution problem, particularly in winter, can be traced back to home heating. Photo: RNZ / Nate McKinnon
Recently the air quality in parts of Canterbury has been rated 'unhealthy' using the air quality index, which measures the levels of particulate matter in the air.
But what does poor air quality actually mean for our health?
University of Otago environmental epidemiologist Professor Simon Hales told RNZ's Nights the source of the pollution, particularly in winter, is generally home heating.
"The reason why it's a problem in winter is because in Christchurch there is a kind of, the city is somewhat bowl-shaped with the Port Hills on one side, and there tends to be sort of a very calm night with the temperature inversion, which is a bit like having a lid on the city. So all the smoke that comes out of people's chimneys is trapped, and that's what leads to the very high level."
Hales said Christchurch's air quality had improved since he lived there 30 years ago, but still needed to improve further.
"The World Health Organization (WHO) has a guideline level for the daily level of PM2.5 fine particle pollution, and that's 15 micrograms per cubic metre," he said.
"About 15 percent of the days over the past five years have been over that guideline level. And in the last three months, about 43 days."
That means, in the last three months, Christchurch's air has had over the WHO-recommended daily level of particle matter in its air about 47 percent of the time.
"There is also an annual guideline which is five micrograms per cubic metre. And in fact the annual average PM 2.5 in Christchurch has been about nine micrograms per cubic metre, so nearly double the WHO guidelines," Hales said.
While polluted air was unlikely to noticeably affect young and fit people, those with chronic diseases, particularly heart and lung related, might notice their symptoms getting worse temporarily.
However, the short-term effects were only part of health impact, he said.
"Over weeks and months of exposure, it's making people who are currently healthy gradually less healthy. So it's actually inducing disease or worsening disease in people who otherwise would have been healthy. And this relates particularly to heart disease and lung disease, but there's an increasing number of different diseases that we're realising are related to air pollution exposure."
And it's not just woodsmoke leading to the poor air quality. Nitrogen dioxide (NO₂), which comes mainly from road traffic, is also a big issue, Hales said.
"In fact, we recently did a study which suggested that the NO₂ was actually more of a problem in terms of its overall health impact, causing over 2000 premature deaths per year."
The same study, published in 2021, revealed that particles mainly from home heating contributed to about 1000 deaths.
The main solution was to switch to cleaner fuels, Hales said. That should not be a problem for a wealthy country like New Zealand, which had abundant hydropower resources, he said.
A similar shift was needed in regards to transport.
"We need to change the modes by which we get about mostly.
"We still use personal cars, mostly fossil fuel-powered cars, and we need to switch both to clean vehicles, EVs for example, but also we need to switch the mode so that people are not relying so much on personal cars, but also using public transport and active transport, so walking and cycling."
New Zealand had mixed results when it came to the WHO's guidelines, Hales said.
"If you look in global terms, then New Zealand is doing pretty well. We're not meeting all of the guidelines all of the time, but we are getting close and in many places we do meet the guidelines for most of the time, so that's something that many countries can't say.
"On the other hand, I think we need to be doing more. We need to have more incentives for the kind of policies that I was suggesting before."
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