A new air pollution investigation has found Auckland to have higher levels of a harmful compound than a Japanese city it was compared against – with cars to blame.

The study, published in the journal Atmospheric Pollution Research, analysed a measure of fine particulate matter, called PM2.5, for two toxic compounds that stemmed from the burning of fuel - polycyclic aromatic hydrocarbons (PAHs) and their nitrated derivatives (NPAHs).

The compounds, which could be absorbed by the lungs and into the bloodstream, have been shown to affect the respiratory, central nervous and cardiovascular system.

They were also of concern for their cancer-causing and gene-changing properties.

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AUT PhD student Egide Kalisa compared PAH and NPAH levels in Auckland, and at Tapora north of the city, with those recorded at seaside Kanazawa in Japan's Ishikawa Prefecture, and at rural Wajima nearby.

Kalisa chose to compare the sites as both had similar geographic characteristics, along with prevailing westerly winds.

Pollution levels were much higher at urban sites than the rural ones.

While his findings showed that levels of PM2.5 at all sites were generally below World Health Organisation limits, their chemical compositions like PAHs and NPAHs could still pose problems to vulnerable populations.

Further, his data revealed cars to be the main source of NPAHs, which were found to be at higher concentrations in Auckland, measuring 48.2 picograms per cubic metre of air (pg/m3), than in Kanazawa (33.45pg/m3).

In Auckland, the lifetime total cancer risk calculated from PAHs and NPAHs also slightly exceeded guidelines used by the US Environmental Protection Agency.

Kalisa said a toxicological analysis of NPAH data was urgently required to better understand the potential health impacts.

AUT PhD student Egide Kalisa compared air pollution levels between Auckland and Kanazawa, a geographically similar city in Japan. Photo / Fiona Goodall
AUT PhD student Egide Kalisa compared air pollution levels between Auckland and Kanazawa, a geographically similar city in Japan. Photo / Fiona Goodall

The Rwanda-born researcher, whose parents both died from respiratory disease linked to indoor air pollution, had earlier shown how heating and heavy traffic brought a high concentration of NPAHs, especially in winter.

The new findings followed an Auckland Council report last year that found pedestrians and workers in Queen St were being exposed to high levels of "black carbon", or ultra-fine carbon particles associated with a number of health problems.

The emissions – blamed on higher diesel emissions from older buses, trucks, ferries and ships – were found to be more than three times greater than Canadian cities and twice as high for concentrations in major European, UK and American cities.

Nationally, air quality was good in most places and at most times of the year, but in cooler months, emissions from home heating could raise to levels above standards and guidelines.

A recent Government stocktake also found how 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.

Unless the world tackles climate change, deaths caused by air pollution are expected to increase by about 60,000 globally by 2030 - and 260,000 by 2100.