Particulate matter (PM) is a collective term used to describe very small solid or liquid particles in the air, such as dust, smoke or fog. A PM10 particle is less than 10 microns in diameter, or one-fifth of the diameter of human hair.
Most PM10 in New Zealand comes from burning solid fuels (ie, coal and wood) for home heating. This, along with the more frequent settled weather conditions during winter, is why most peak PM10 levels occur during this time of year. Exhaust emissions from vehicles are another significant source of PM10 in some cities.
Other sources of PM10 include emissions from vehicles and industry. There are also natural sources of PM10 such as pollen, mineral dust and sea salt.

These webpages track air quality against a national standard that sets an acceptable daily level for PM10 and a New Zealand guideline that sets an acceptable annual level for PM10. Regional councils currently monitor 44 areas where air quality is likely to or known to breach the PM10 standard – these areas are known as airsheds. In most cases, airsheds are single towns or cities, though some group a number of towns together.
Home heating is the most common source of PM10 air pollution in New Zealand.
Car owners can obtain more information on how to reduce vehicle exhaust emissions at Ministry of Transport website
Information on the limitations of the air quality indicator.
Last updated: 2 August 2011