Particles
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 microns (10 µm or 10 micrometres) across – because we easily inhale these small particles into our lungs.
The diagram below compares the size of these particles (PM10 and PM2.5) to a strand of hair and some beach sand. They are tiny – too small for the human eye to see. The amount of exposure to pollutants is often measured in units of micrograms of substance per cubic metre of air (µg/m3).
Abbreviations
- TSP
- total suspended particulate
- PM10
- particles with a diameter less than 10 microns
- PM2.5
- particles with a diameter less than 2.5 microns
Sources
TSP comes from sources like dusty roads, soil tiling, quarries and fuel combustion.
PM10 and PM2.5 come from sources such as burning coal, oil, wood and light fuel oil in domestic fires, transportation and industrial processes. Natural sources of particles include sea salt, dust, pollens and volcanic activity.
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 remove particles larger than 10 µm in size. Particles smaller than 10 µm can penetrate into the lungs, where they cause problems and affect our health.
Some of the most common health effects include irritation of your eyes, throat and lungs. For people with existing respiratory conditions, such as asthma or bronchitis, breathing in particles can make the conditions worse.
Particles can also reduce your capacity to resist infection. Studies show that particles can increase the number of hospital admissions and emergency department visits, school absences, lost work days and restricted activity days.
Studies in the United States and Europe show a correlation between levels of particles and the number of people who die each year (the mortality rate).
Groups that are most sensitive to particle pollution
Healthy children, adults with obstructive lung disease, asthmatics, and the elderly.
Guideline value to protect health
In any 24-hour period, the average concentration of PM10 in the air should not be more than 50 µg/m3. The average annual concentration of PM10 should not exceed 20 µg/m3. There is no guideline value for PM2.5 yet.
Effects on ecosystems
Particles can also affect plants although there is little information available. In very dusty environments, particles may affect photosynthesis in plants by settling on leaves and reducing the amount of sunlight reaching the leaf.
Effects on visibility
Fine particles in the air reduce visibility because they scatter or absorb light. This is usually associated with small particles or certain gases in the atmosphere and can occur at night or during the day.
Usual levels in New Zealand
In most New Zealand cities and towns, PM10 levels are usually about 25-35 µg/m3 (24-hour average). This is below the guideline value. However, some cities and towns have quite bad particle pollution, especially in winter with recorded levels of up to 500 µg/m3 (24-hour average). For example, Christchurch and Nelson often experience high levels of PM10 in winter when particles from residents’ home fires get trapped close to the ground by temperature inversions. In rural areas, levels are usually around 2 µg/m3 (24- hour average).
For more information about levels in New Zealand, check out Emission Inventories for PM10 in New Zealand.
Areas where particles may cause problems
Particle pollution can affect whole urban areas, especially during winter smog conditions, and smaller local areas such as around dusty activities or industrial discharges.
Last updated: 9 January 2008
