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Harmful substances - Particulate matter

Characteristics and impact of particulate matter

Particulate matter (PM) is a complex mixture of airborne particles that differ in size, origin and chemical composition, all of which are <10 μm in size. Fine particles are desperse in air and can move freely over great disatnces. Particulate matter does not always land near the source, causing entire countries to be polluted. Particulate matter concentrations are highest near locations of emission, such as highways and power plants. Most countries contribute to aiborne particulate matter pollution in other countries.

In the past couple of years particulate matter has recieved media attention, concequential to the discovery of thousand of people dying young of particulate matter introduced health effects. This includes both short-term and long-term effects.

Particulate matter does not only cause health effects, it also plays a role in the greenhouse effect and global warming, because of its contribution to cloud formation.


Particulate matter is released from natural sources, such as volcanic eruptions, seasalt, or soils. Anthropogenic sources, such as car exhausts, industry, shipping and coal and ore fabrication, cause increases in airborne particluate matter concentrations on many locations. Power plants add to emissions of particulate matter. Emissions from private houses stem from fire places and barbecues. Dutch epidemiologists state that emissions from traffic, particularly from diesel engines, are most damaging to human health.

Example of particulate matter for part of the US, where green = below standards, yellow = moderate pollution


Three separate groups of particulate matter are distinguished, according to particle size:

- PM10: diameter 2.5-10 μm (road dust and particles from worn out engines and breaks)
- PM2.5: diameter <2.5 μm (from diesel engine exhausts)
- Diameter <0.1 μm (EC; elementary carbon)

A distinction is also made between primary and secundary partciles. The distinction depends upon the formation of particles in air. Primary particles are formed by friction, wind or fossil fuel burning. Secundary particles are formed during chemical reactions in air of acid substances to salts. Primary particles may adsorb to secundary particles.

According to the EPA only PM2.5 is harmful to human health, because larger fractions attach to small hairs in the respirational tract, and are subsequently released upon clearing one's throat. Consequently, standards for particulate matter size 2.5 and smaller are stricter than for larger particles.


In the past 20 years particulate matters emissions in industry decreased after implementation of dust and soot filters. However, the decrease was partly annulled by increasing emissions in other sectors. Standards for particulate matter are relatively strict, because of the health hazard.

Particulate matter is regulated by the Environmental Protection Agency (EPA). Two separate standards for fine particles are included in the Clean Air Act. Primary standards are based upon health effects caused by specific partciles, whereas secundary standards are based upon welfare impact of particulate matter, preventing visibility impairment, and damage to crops, animals and buildings. This year, the 24-hour standard for PM2.5 was decreased from 65 to 35 micrograms per cubic meter, and the standard for PM10 was set to 150 micrograms per cubic meter.

In Europe standards for particulate matter are regulated by the World Health Organization (WHO), and are set to 40 micrograms per cubic meter for PM2.5. By 2010 this will be decreased to 20 micrograms per cubin meter.

Health effects

Particulate matter causes health effects upon inhalation. The severeness of health effects is determined by size, composition and concentration. Research in both Amerika and Europe demonstrated a clear correlation between particulate matter concentrations and health effects. Exposure may cause heart and lung disease, and may worsen acute and chronic bronchitis and asthma.

Young asthma patient

The risk of health effects is larger for certain groups of individuals. Examples are cara patients, elderly people with respiratory defects, young children and people that do heavy physical labor. High levels of particulate matter may not only affect these groups of people; this causes the entire population to be at risk.

A particulate matter mask


EPA: http://www.epa.gov/oar/particlepollution/

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