environment

‘Brown haze’ making Kiwis sick

People are being hospitalised by deadly “brown haze” despite New Zealand's air getting cleaner, reports Eloise Gibson

Smog warnings regularly keep people indoors in Delhi and Beijing, but so-called “brown haze” is putting people in hospital even in relatively unpolluted Auckland.

The smog that can collect over cities on still, cold days in winter is the most immediately deadly form of urban air pollution – and now researchers have tracked its impact on our biggest city’s hospitals.

The impact led the authors to suggest a smog early warning system, so people could be pre-warned as they are in more polluted cities elsewhere.

“Medical institutions and practitioners could benefit from improved capacity to predict Auckland’s brown haze events in order to prepare for the likely increases in respiratory admissions over the days ahead,” they said.

Researchers at the University of Auckland, Tauranga Hospital and Auckland Council tracked Auckland District Health Board hospital admissions over 11 years and compared them to air samples taken from West Auckland’s busy arterial route, Lincoln Road. Lincoln Road is generally a good proxy for air around the city, they said.

The study, published last year, found the number of people admitted for breathing-related sicknesses tended to rise by about 6 percent around five days after a ‘brown haze event’ – the name the researchers gave to the fog of pollution that is linked to asthma, premature births, lung cancer and sicknesses like bronchiolitis in babies in cities the world over.

Auckland experienced ‘brown haze’ between three and 11 times a year during the decade to 2011, they found.

But a report out today from Statistics New Zealand and the Ministry for the Environment shows Auckland is generally less polluted than several smaller towns and cities, particularly in the South Island.

That’s because the main source of the riskiest kind of air pollution is home wood-burners, which are more common in the South Island and, presumably, used more often in colder places. Auckland is the only city in New Zealand where cars, not fires, are the main danger to air-breathers.

The last decade saw a slight reduction in the number of New Zealanders estimated to have died from breathing dirty air, but that was probably because of more people moving to Auckland from dirtier air-sheds, not because of cleaner air, the Our Air report concluded. 

There was good news in the air report for the nation’s lungs and hearts: the unhealthiest pollution is lessening almost everywhere that regional councils have good records of air samples, at least in places where air analysts can see a clear trend. The air quality stock-take follows similar reports on water quality and other environmental measures.

Councils track several kinds of air pollution, but the most immediately risky to people is particulate matter – found in brown haze, or smog. Larger particles are dubbed PM10 and finer, more damaging, particles are known as PM2.5. Past studies in Christchurch and elsewhere have linked these particles to spikes in hospitalisations. Nationally, each year, it’s been estimated that PM10 exposure is responsible for at least 1175 premature deaths and 607 extra hospital admissions for respiratory and cardiac illnesses.

Small but deadly

PM10 is better-tracked and better-studied than PM2.5 but it’s the smaller, less-studied particles that are more dangerous to people’s health, because they penetrate past the throat and nose and go deep into the lungs, says the Our Air report.

According to the World Health Organisation, the more particulates people breathe and the longer they breathe them for, the higher their long-term risk of dying from a heart or lung disease.

“Physiological changes can occur within hours of exposure to high concentrations, and can be associated with premature death and illness immediately after exposure and in the following days,” the WHO said in 2013.

The report lists more details: Breathing particulates can cause anything from mild, reversible coughing and feeling out of breath to disease and early death from cardiovascular and respiratory problems, such as heart attack, stroke, or emphysema. It can also cause lung cancer and exacerbate asthma, and is particularly risky to young children, elderly people and people who already have a heart or lung problem. In foetuses and new babies, high levels of the pollutants in air have been associated with pre-term birth, underweight newborns, and a sickness called bronchiolitis that makes it hard for young babies to breathe.

The report notes that few studies before now have measured the health impacts on New Zealanders, but a study last year using data from the ‘Growing up in New Zealand’ child cohort study found that living in a neighbourhood with a higher density of wood burners was associated with a 28 percent higher risk of children going to hospital for a non-accidental emergency.

Because it can be hard to pin particular deaths on air pollution, health researchers use models to estimate how many people die prematurely each year in New Zealand because of dirty air.

That modelling estimates that, for every 100,000 New Zealanders aged older than 30, 27 adults died prematurely from bad air in 2016, compared with 29 in 2006 – a slight improvement. That only accounts for the effect of the larger particles, PM10, not PM2.5 effects.

However the report doesn’t credit the slight reduction in estimated deaths with any air pollution-cutting measures. Instead, it is likely because more people moved from other places to Auckland, where PM10 concentrations are lower, it says.

Helpfully, in that case, Auckland air samples show a long-term decrease in dangerous particulates spanning several decades, though the city still experiences risky spikes.

Other urban areas are more mixed, though the general trend is towards cleaner air.

The Our Air report says PM10 concentrations were measured at 96 mostly-residential sites across the country between 1996 and 2017. Of those only 45 had enough data to calculate trends. Of the 45, 18 recorded decreasing pollution during the risky winter months between 2007 and 2016 (the most recent year for which the government has complete data).

Others had no trend, or were getting worse - but only in summer, when air pollution isn’t such a big problem.

The exception to generally improving winter air quality was Blenheim, where pollution has worsened on average during the cold months.

Despite the overall cleaner air, more than half of places tested had sometimes topped safe levels of particulates. People living in 30 out of the 51 places monitored would have breathed air that exceeded national standards for PM10 pollution at some point over the three years from 2014-2016, with the worst places being Alexandra (51 times in 2014), Arrowtown (48 times in 2014), and Cromwell (48 times in 2014). The Government announced today that it will review the national standards.

PM2.5 is not as well-monitored as PM10, despite being more dangerous. But, of the handful of sites with enough data to calculate trends in the decade up to 2016, four out of the five were getting cleaner in winter when it came to PM2.5 levels. The highest average concentrations were generally found in small and medium-sized towns like Masterton, Geraldine and Timaru, likely driven by emissions from residential home heating and by natural features (topography and weather) that favour the build-up of pollutants, says the report. Timaru, Masterton and St Albans in Christchurch had, at times, topped the WHO guidelines for long-term exposure to PM2.5.

Except for Auckland, wood fires were the main smog-creator. In 2015, the latest year with numbers available, burning wood for home heating was the single biggest source of both PM10 and PM2.5, especially in urban areas during winter. A third of North Island homes and almost half of South Island homes had wood fires in 2013, and a further few percent of houses burned coal for warmth. Car fumes and emissions from manufacturing and construction were next.

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