New Zealand has some of the cleanest and safest air on the planet, a new World Health Organisation report suggests.
The report analysed data from more than 100 nations, comparing exposure to ambient air pollution and related death and illness.
It showed New Zealand was either in the top five or 10 nations with the best results for concentrations of PM2.5 - a key measure of air pollution - along with rates of deaths, disease and illness that could be attributed to pollution.
However, Associate Professor Simon Hales of Otago University's Department of Public Health questioned whether the report's methods accurately reflected rates in smaller countries such as New Zealand.
"Their estimates of PM2.5 exposure use data from satellites, which are excellent for large countries with little surface air pollution monitoring data, but do not perform so well at local scale in small countries like New Zealand," Hales said.
The resolution of their data is of the order of 10km, which was too coarse for most New Zealand urban areas, he said.
"The study authors did not assess health impacts of exposures below 5.9 μg/m3.'
"Again, this makes sense if exposures are high, as in countries with a lot of heavy industry or using biomass for heating and cooking.
"It is not so appropriate for New Zealand, since we know from epidemiological studies of mortality that the comparatively low levels of exposure do have a substantial health impact here.