This page provides information on particles in the air and their effects on our health, ecosystems and visibility. It includes usual levels in New Zealand, and standards and guidelines values to protect human health.
This page has not yet been updated to reflect changes as a result of Our air 2018 report.
Particles found in the air we breathe vary greatly in size. The greatest health hazard from particles comes from the smallest ones – less than 10 micrometres (10 µm or 10 microns) across – because we easily inhale these small particles into our lungs.
These are classified as:
|PM10||particles with a diameter of 10 micrometres or less|
|PM2.5||particles with a diameter of 2.5 micrometres or less|
|TSP||total suspended particulate|
The diagram below compares the size of PM10 and PM2.5 particles to a strand of hair and a type of beach sand. They are tiny – too small for the human eye to see.
Source: Ministry for the Environment
The amount of exposure to particles is often measured in units of micrograms of substance per cubic metre of air (µg/m3).
|PM10 and PM2.5|| |
Fuel combustion such as burning coal, oil, wood and light fuel oil in domestic fires, transportation and industrial processes.
Sources include dusty roads, soil tiling, quarries and fuel combustion.
Natural PM10 and PM2.5 particles include sea salt, dust, pollens and volcanic ash. PM2.5 is also formed through chemical reactions in the atmosphere.
Effects on health
When we breathe in, the hairs in our nose and air passages generally remove particles larger than 10 micrometres in size. Particles smaller than 10 micrometres can penetrate into the lungs and affect our health.
Some of the most common health effects include irritation of eyes, throat and lungs. Breathing in these particles can also make existing respiratory conditions such as asthma or bronchitis worse.
Studies show that breathing in these particles can increase the number of hospital admissions and emergency department visits, school absences, lost work days and restricted activity days.
International and New Zealand studies show a correlation between levels of particles and the number of people who die each year (the mortality rate).
Groups most sensitive to particle pollution
|adults with obstructive lung disease|
Standards and guideline values to protect health
In any 24-hour period the average concentration of PM10 in the air should not be more than 50 µg/m3 as per the National Environmental Standards for Air Quality.
The PM10 annual average concentration should not exceed 20 µg/m3 as per the National Ambient Air Quality Guidelines.
The 24-hour average concentration should not exceed 25 µg/m3 and the average annual concentration should not exceed 10 µg/m3, as per the World Health Organization guidelines.
Effects on ecosystems
Air pollutants can settle out of the air onto land and water bodies. From the land they can wash into and concentrate in waterways or be taken up by plants and animals.
When air pollutants come into contact with plants they can impair plant growth. If animals inhale them they can be affected in the same way as humans.
Effects on visibility
Particles in the air reduce visibility because they can scatter or absorb light. Reduced visibility can occur at night or during the day.
These pictures show a comparison of visibility degradation caused by winter smog (picture on the left) with clear spring air in Christchurch.
Source: Canterbury Regional Council
Usual levels in New Zealand
In most New Zealand cities and towns, PM10 levels are generally below the 24-hour standard and annual ambient air quality guideline value.
Some cities and towns can have quite bad particle pollution, especially in winter. In 2013, the highest PM10 24 hour average concentration recorded at one location was close to 140µg/m3 in 2013.
For more information about particle levels in New Zealand see Environment Aotearoa 2015.
Areas where particles may cause problems
|urban areas|| |
especially during winter smog conditions when particles from home fires get trapped close to the ground by temperature inversions
|localised areas|| |
(eg, where there are dusty activities or industrial discharges).