Air pollution from fires, vehicles and industry kills 1170 people prematurely each year and causes $4.28 billion in social costs, researchers have estimated.
Natural sources of air pollution, such as sea spray and wind-blown dust, lead to a further 1136 early deaths, producing a national toll of 2306, say the researchers from four private consultancies and two universities.
Home-heating fires are the leading cause of the man-made air-pollution deaths, except in central Auckland, where exhaust from motor vehicles is the top killer.
The estimates are based on exposures to tiny pollution particles, less than one-hundredth of a millimetre in diameter. They can lodge in the airways and lungs; the smaller "ultra-fine" particles can even enter the bloodstream. The particles can cause or contribute to various sicknesses, such as bronchitis, lung cancer, asthma and heart attacks.
The death estimates, only just made public, are based on data from 2006. They update research published in 2007, which was based on 2001 data from fewer places than the new report.
Since the two reports are not directly comparable, the researchers revised the older findings with their updated approach. This increased the older report's estimate of 901 premature deaths a year from human-caused air pollution, to 1058.
"All [man-made] sources except motor vehicles show a predicted increase in health impacts between 2001 and 2006," the report says, "largely in response to the increase in population combined with minimal or no changes in emissions.
"The reduction in motor vehicle impacts reflects the significant and genuine improvements made in fuel quality and emissions standard requirements introduced after 2001.
"Comparable improvements have occurred in domestic fire emissions in response to the introduction of the woodburner standards and various insulation and clean-heat retrofit programmes ... ."
Areas such as Nelson and Christchurch experienced significant reductions in the levels of fine-particle air pollution from 2001 to 2006, but changes in most areas were after 2006.
"For a lot of places their concentrations [of pollution] have been going down appreciably since 2006 but we weren't able to capture that in this study," lead researcher Dr Gerda Kuschel said yesterday.
These later changes are expected to show up as improvements in any new updates.
One was planned for last year in line with the five-yearly Census, but the Census has been delayed until next year because of the Christchurch earthquakes. The social cost per person of human-caused air pollution is $1061 a year, of which 56 per cent is from domestic fires, 22 per cent from motor vehicles, 12 per cent from open burning and 10 per cent from industry.
The only region where domestic fires don't dominate is Auckland, particularly in the old Auckland City Council area, "where motor vehicle health impacts are nearly twice those of domestic fires".
But because the researchers could not robustly assess nitrogen dioxide levels, they expect the latest figures probably underestimate the impact of motor-vehicle air pollution.
The Automobile Association said the reduction of sulphur content in petrol and diesel and rules preventing the importation of older Japanese vehicles would have improved emissions.
Sulphur in diesel, a big source of fine particles, has been cut to 10 parts per million, from 3000 in 2001.