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Tiny particles of marine salt and secondary sulphate - carried hundreds of kilometres on the wind from the oceans and volcanoes - form a significant proportion of the air that Aucklanders breathe, a pollution study has found.
The most comprehensive of its kind in New Zealand, the study, commissioned by the Auckland Regional Council, aims to find out the composition of particles in the air.
It follows the ARC's setting of a 58 per cent reduction target for vehicle and domestic discharges of particulate below 10 microns by 2013 so air quality can meet the national standard.
However, ARC air policy manager Kevin Mahon said the present inventory of air emissions estimated that households - through heating, lawn mowing and painting - are responsible for 39 per cent of man-made sources of sub 10 micron particulate in emissions. This could rise to 64 per cent on a winter's day.
Particles collected during a year at five sites - Queen St, Kingsland, Takapuna, Khyber Pass Rd and Penrose - and analysed by Geological and Nuclear Sciences (GNS Science) had enabled a better understanding of "background" levels of particulate and their sources.
Mr Mahon said significant new information showed background sources, such as marine aerosol (airborne salt water particles), need to be carefully considered when setting reduction targets to meet the air quality standard.
Background levels of particulate had to be added to those of man-made sources of solid fuels burning, motor vehicles and industrial discharges, because all sources combined to form a concentration of particulate matter in the air.
Mr Mahon said the study showed that 40 per cent of sub 10 micron particles came from marine aerosol and secondary sulphate - from sulphur oxide gas emitted by industry and volcanic activity.
These sources produced 25 per cent of the fine sub 2.5 micron particles measured by air monitors.
Emissions from motor vehicles and burning of solid fuels were primary man-made contributors to both sizes of particulate.
Mr Mahon said marine salt was in highest concentrations in summer and this explained why pollution standards were exceeded in summer, when there were no domestic fires.
The fine particles could be carried large distances from the Tasman Sea and Southern Oceans, with a small component coming from the north east, the Pacific Ocean.
Course particles came from the sea close to Auckland.
Most particles of secondary sulphate in Auckland's air were sub 2.5 micron and were most concentrated in the summer.
High sulphate concentrations at all monitoring sites in September 2006 were investigated.
"This analysis found that the sulphate containing air mass was produced by an original sulphur dioxide gas plume which may have been due to volcanic emissions from White Island or potentially other volcanic emissions in the Central Plateau and Rotorua area," Mr Mahon said.
Monitoring of White Island emissions at 500 tonnes a day were two to three times higher than average over the period September to November 2006.
ARC Chairman Mike Lee said he had never heard that marine salt was an issue in air quality and any suggestion that it be included in setting pollution standards would have to be thoroughly scientifically and medically proven before adopted.
Professor Alistair Woodward, head of the school of population health at Auckland University, said the study was interesting and it would be helpful to know the composition of particles in the air.
"But it is more difficult to tell what the health implications would be," he said.
"Is it the chemistry of particles or is just having little things inside your lungs that irritate airways?"
Professor Woodward said very small flinty bits of matter getting into the small airways of the lungs could cause inflammation in the lungs.
