Respirable particles

Substance name	Respirable particles
CASR number	Not applicable
Molecular formula	Not applicable
Synonyms	Dust, particulate matter, inspirable dust, respirable dust, smoke, mist, PM10.

Physical and chemical properties

Dust particles of any substances that are less than or equal to 10 micrometres diameter. Particles in this size range make up a large proportion of dust that can be drawn deep into the lungs. Larger particles tend to be trapped in the nose, mouth or throat. Size is not an absolute criterion as thin flakes and fibres longer than 10 micrometres may be part of a PM₁₀ sample because of their aerodynamic properties.

These vary depending on the source of the dust. It is important to note that PM10 is not one particular substance but a classification of dust by size rather than by chemical properties.

Common uses PM₁₀ is not used for any application; it is derived from fugitive, industrial and combustion sources.

Sources of emissions

Point sources Respirable particles are released from industrial processes through bulk material handling, combustion and minerals processing. The industries using these processes include brickworks, refineries, cement works, iron and steel making works, quarries and fossil fuel power plants.

Diffuse sources, and point sources included in aggregated emissions data Respirable particulate matter is released from a wide range of sources that produce particles or dust. Examples are lawn mowing, wood stoves, fires and cigarette smoke. Respirable particulate matter can also occur in wind-generated dust, though this dust tends to be relatively coarse. Fine secondary aerosols generated as part of photochemical air pollution and some forms of wintertime haze will register in the measurement system as PM₁₀.

Natural sources Particulate matter can be generated by wind from open soil, fires or volcanic activity.

Mobile sources Vehicles will generate PM10 (dust) either from direct emissions from the burning of fuels (especially diesel powered vehicles) or from the action of tyres or vehicle-generated air turbulence on roadways. Dust may also be generated from the action of wind on the dusty material that the vehicle may be carrying, although this will rarely be in the PM₁₀ range.

Consumer products that may contain respirable particulate matter Respirable particulate matter is not generally included intentionally in any product but may be present as part of the product (eg as part of talc or other powder products).

Health effects

How might I be exposed to respirable particulate matter? All people are continuously exposed to some extent except in special filtered environments. Exposure will occur even in pristine environments. Exposure may be higher in urban and industrial areas due to an increase in the number of sources; however, high levels may also occur in natural environments.

By what pathways might respirable particulate matter enter my body? Dust in the PM₁₀ size range is commonly present in air and may be drawn into the body with every breath. In the lungs it can have a direct physical effect and/or be absorbed into the blood. Dust, not only the PM10 fraction, may also be deposited in the mouth, throat or nose and be ingested.

Health guidelines National Ambient Air Quality Standards and Goals:

• one-day averaging period maximum concentration: 50 mg/m³ (0.00005 g/m³)
• maximum allowable exceedances 5 days per year, to be achieved within 10 years.

What effect might respirable particulate matter have on my health? Recent epidemiological research suggests that there may be no threshold below which health effects do not occur. The health effects include:

• toxic effects by absorption of the dust into the blood (eg lead, cadmium, zinc);
• allergic or hypersensitivity effects (eg some woods, flour grains, chemicals);
• bacterial and fungal infections (from live organisms);
• fibrosis (eg asbestos, quartz);
• cancer (eg asbestos, chromates);
• irritation of mucous membranes (eg acid and alkalis); and
• long-term deleterious effects on lung function causing marginally increased death rates and sickness in sensitive people.

The factors that influence the health effects are:

• the composition of the dust and its health effects;
• the concentration of the dust;
• the size of the dust (smaller particles tend to have more severe effects because they may be inhaled more deeply into the lungs); and
• the duration of exposure (possibly in years).

Environmental effects

Environmental fate PM10 is very fine and light and is, therefore, easily entrained into the air by wind or disturbances. Chemical changes may occur in the form of reactions with other substances depending on the composition of the dust. Particles may stick together or break apart, changing the size distribution over time.

Environmental transport Once in the air, respirable particulate matter generally takes a long time to settle. The dust may be washed from the air by rain or snow. When it settles on land, it may settle permanently or be re-entrained. In water the dust may settle or dissolve, or both.

Environmental guidelines The only national guidelines are the National Ambient Air Quality Standards and Goals (see above under 'Health guidelines'.