United Nations Environment Programme

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Pollutants: Particulate matter (PM)


(Suspended PM, PM10, PM2.5 and PM0.1):

Solid or liquid particles from unburnt matter are always emitted from combustion processes. The emission of such particles have been defined and measured in various ways. Generally, suspended particulate matter (SPM) refers to particles in the air of all sizes. SPM is a complex mixture of organic substances, present in the atmosphere both as solid particles and liquid droplets. They include fumes, smoke, dust and aerosols. Health impacts of PM vary depending on the size and the concentration of particles. For regulatory purposes and for estimating health impacts, PM is measured and classified by what is called the respiratory fraction of particles, for example, PM10 and PM2.5.


  • PM10 refers to particles with a diameter less than 10 microns. These are commonly called coarse particles - they contain dust from roads and industries as well as particles formed under combustion. Depending on their size, coarse particles can lodge in the trachea (upper throat) or in the bronchi.
  • PM 2.5 refers to particles with a diameter of less than 2.5 microns. These are usually called fine particles and contain secondary aerosols, combustion particles and re-condensed organic metallic vapour, and acid components. Fine particles can reach all the way down to the alveoli in the lungs.
  • PM0.1 refers to particles with a diameter less than 0.1 microns, and are called ultra-fine particles. Ultra-fine particles - still in the early stages of research - are usually exhaled but can penetrate into the bloodstream.

Visible smoke is comprised of particles of PM10 size or larger. The particles with the greatest health effects are those within the "respirable range", that is between PM10 and PM0.1. The respirable range contains particles that can penetrate deep into the lungs and deposit there; particles smaller than PM0.1 are usually exhaled. Fine and ultra fine particles (PM2.5 and PM 0.1) are not visible to the eye (2.5 microns is approximately 1/30th the size of a human hair).

Sources of Particular Matter:
Particles are formed during the combustion process of motorized vehicles. Diesel vehicles and 2-stroke motorcycles without emission control technologies tend to emit more particles. Diesel vehicles also emit a large number of fine and ultra-fine particles. Moreover, particles are formed by the transformation of gaseous emissions like oxides of sulphur and nitrogen and VOCs, into secondary pollutants.

Other sources of particular matter include: burning of wood, coal, oil and gaseous fuels; burning of coal refuse, agricultural refuse, and municipal solid waste; fly-ash emissions from power plants; smelting and mining activities; asbestos factories; metallurgical industries; ceramic industries; glass industries; cement industries; etc.

Non-human-induced sources of include forest fires, volcanic eruptions, wind and dust storms, salt sprays, etc.

Human Health Effects of Particular Matter:
Fine particles of less than 3 microns in diameter enter the nose and throat, reach the lungs, and cause breathing problems and irritation of the lung capillaries.

Particulate matter causes respiratory morbidity, deficiencies in pulmonary (lung) functions including decreased lung function (especially in children), and lung cancer with the consequence of increased mortality. Chronically reduced lung capacity (emphysema) among the urban population is also a major risk.

Environmental Effects of Particulate Matter:
The environmental effects of particulate matter include accelerated corrosion of metals, as well as damage to paints, sculptures, and soil-exposed surfaces on man-made structures. The extent of damage depends on the physical and chemical properties of the particulate matter. Particulate matter has also the potential to modify the climate through the formation of clouds and snow. Particles also contribute to acid deposition and may absorb solar radiation and impair/reduce visibility.


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