Warming our homes in winter with wood and coal, and the fumes we pump from our cars, remain the biggest threats to New Zealand's air quality. Photo / File
Warming our homes in winter with wood and coal, and the fumes we pump from our cars, remain the biggest threats to New Zealand's air quality.
But a new report out today shows pollution levels have been dropping in many areas.
The latest stocktake report by the Ministry for the Environment and Stats NZ showed that while some problems persisted, progress has been made and levels of some pollutants were declining.
"The report shows that using wood and coal burners to heat homes in winter continues to cause issues in some places," Government Statistician Liz MacPherson said.
"This remains the largest single cause of human-generated poor air quality in New Zealand."
While air quality was good in most places and at most times of the year, in cooler months, emissions from home heating could raise to levels of human-made source of particles suspended in the air, or particulate matter (PM), above standards and guidelines.
This was especially the case when weather and landscape helped PM to build up.
The national emissions inventory indicates burning wood and coal for home heating was the biggest single source In 2015, making up one quarter of PM10 (particles less than 10 micrometres) and 33 per cent of PM2.5 (particles less than 2.5 micrometres).
Data from monitoring sites indicate air quality is poorer in autumn and winter when temperatures were cooler.
From 2007 to 2016, 79 per cent of instances when PM10 and PM2.5 were higher than guidelines occurred during winter.
However, monthly average PM10 concentrations between 2007 and 2016 have seen increasing trends in 17 of 39 monitoring areas, or "airsheds", in winter, when home-heating emissions were at their highest.
Arsenic levels in our air also peaked in winter when people burn treated wood for home heating.
"The report also shows vehicle emissions as a leading cause of poor air quality in some places," McPherson said.
Vehicle emissions contributed to poor air quality in places, particularly for nitrogen dioxide pollution, which could cause serious health problems.
While data indicated vehicles were the single biggest source of human-generated nitrogen oxides in 2015, accounting for 39 per cent, it also showed a slightly decreasing trend in Auckland, Bay of Plenty, Hamilton, Northland, and Wellington between 2004 and 2016.
MacPherson called this a "welcome sign", and something that had led to a slight health improvement.
International studies show that air pollution can affect people's health in many ways.
Effects included shortness of breath and coughing, heart attack, stroke, diabetes, and
premature death.
New Zealand-specific studies on the health impacts were limited, but modelled data provides information on the changes over time.
In 2016, modelled data estimated the number of premature adult deaths per 100,000 people from exposure to PM10 in New Zealand was 8 per cent lower than in 2006.
The number of days per 100,000 people when people were not able to go about their regular daily activities was 12 per cent lower.
But relative improvements in air pollution effects appeared to be largely due to more people living in areas with lower PM10, such as Auckland, rather than a drop in PM10.
Climate change, too, would have an impact.
Because ozone was formed through other air pollutants reacting in the presence of sunlight and warmth, an increase in temperature with a warmer climate would speed up the chemical reactions that form ozone and lead to increased concentrations.
Ground-level ozone could have serious human health effects - and an increase would be a particular concern in cities like Auckland, which have high levels of transport emissions that act as precursors to ozone formation.
The additional stress that a warming or drying climate places on ecosystems could increase susceptibility to air pollutants.
It may also increase the frequency of wildfires and the amount of wind-blown dust, which would increase the amount of PM in the air.
In contrast, warmer temperatures in winter would likely result in less wood burning for home heating, lowering PM levels.
The report highlighted some other emerging issues that needed more investigation.
There was increasing evidence for health effects from ultrafine particulate matter - that smaller than 0.1 micrometres - which came mainly from vehicle emissions, but also home heating and forest fires.
Because they could avoid many of the body's defences for PM, a greater proportion than larger-sized particles were deposited in the lung.
Their small size also allowed them to cross into the bloodstream where they could be transported throughout the body, resulting in very different health impacts from larger particles, even causing cellular and genetic damage.
But long-term studies on their health effects and grades to measure them weren't yet available.
The report further singled out ammonia, brought about by farming intensification.
When excess nitrogen from fertiliser was released into the air in the form of ammonia, much of it transformed into ammonium nitrate or ammonium sulphate particles.
These could then be transported far from its source, potentially affecting ecosystems when it settled from the air, or was incorporated in rain drops.
There had been a marked increase in the intensity of farming, especially for dairy, which increased 42 per cent in area between 2002 and 2016.
International research shows that excess nitrogen as ammonia can acidify soil and cause changes in biodiversity by creating nutrient imbalances that favour one species over another, often favouring exotic species over natives.
Because soils in New Zealand tend to be naturally low in nitrogen, even small increases have the potential to harm biodiversity and ecosystems.
As increases in livestock numbers and fertiliser use are recent, it wasn't known how much excess nitrogen was being emitted to the air and subsequently reaching our natural areas.
Yet another potential issue was sulphur dioxide emissions from a growing number of ships visiting the country.
Emissions from shipping also include PM, nitrogen oxides, and carbon monoxide.
Nationally, domestic shipping contributed 20 per cent of sulphur dioxide in 2015, but only 10 per cent of national nitrogen oxides, although it emitted these pollutants in almost equal amounts.
Studies in Auckland had found that sulphur dioxide concentrations were higher near the waterfront and are highest when the wind comes from the direction of the port.
Tracer studies that could "fingerprint" emissions from shipping by measuring nickel and vanadium, which were predominantly associated with shipping emissions, found the highest levels near the water.
The studies also found a shipping sulphate influence at many of the PM monitoring sites around Auckland, even several kilometres away from the port.
Elsewhere, shipping had been identified as the main source of sulphur dioxide emissions in Wellington, and might also be a problem at other ports such as Tauranga and Whangarei, the report suggested.
Some ports also used the pesticide methyl bromide to fumigate logs before export.
Although localised in nature, methyl bromide has been linked to impacts on human health and was recognised as an ozone-depleting chemical that had been phased out by most other countries over the past 15 years.
In 2016, there were 13 users of methyl bromide in New Zealand - the highest reported use was 319.6 tons at Northport – Marsden, which was 31 per cent more than it used in 2012.
Despite the concerns, the Environmental Protection Authority didn't include it among the 40 chemicals it recently selected for reassessment.
While New Zealand had low levels of light pollution and some areas had pristine night skies, all major urban areas now had light pollution, which could affect cultural practices and natural ecosystems.
Based on estimates from satellite data in 2014, 74 per cent of the North Island and 93 per cent of the South Island had night skies that were either pristine or only degraded by light pollution near the horizon.
But light pollution in cities meant more than half of us couldn't see the Milky Way.
"This report paints a series of separate pictures," said the Ministry for the Environment's deputy secretary, Amanda Moran.
"The overall news is good, but we still have some specific issues to address. Progress is being made with those but there's more to do.
"The situation is getting better but it's still not perfect and we must keep working on improvements.
"Clean air to breathe is a key part of well-being for all New Zealanders.
"We know the health impacts from air pollution can be serious, and those with a pre-existing condition such as asthma are more susceptible.
Responsibility for that continued improvement is shared by all: central and local government, industry, communities, and individuals.
"Technology changes, for example improved wood burners or electric vehicles, will help but we also need to change our behaviours, like getting out of our cars and being careful what we burn.
"We need to ensure the National Environmental Standard that covers this area remains fit for purpose and that all areas of government policy-making, such as transport policy or urban planning, take air quality issues into account."
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