Generally, two different approaches are used to measure the amount of dust deposited on a surface- Determination of the soiling of a surface, by a change in its properties and determination of the quantity of dust deposited, by weight
What is dust?
Dust is a generic term used to describe fine particles that are suspended in the atmosphere. Dust comes from a wide variety of sources, including soil, vegetation (pollens and fungi), sea salt, fossil fuel combustion, burning of biomass, and industrial activities. It is formed when fine particles are taken up into the atmosphere (entrained) by the action of wind or other physical disturbances or through the release of particulate-rich gaseous emissions (primary particles). In addition, gases such as sulfur dioxide and oxides of nitrogen may react in the atmosphere over time to form fine particles, such as ammonium sulfate and ammonium nitrate (secondary particles).
Health effects of dust:
The factors that influence the health effects of dust are:
- Size of the dust particles
- Composition of the dust particles
- Concentration of the dust particles in the air
- Duration of exposure (possibly in years) to the dust particles.
There is considerable debate over the relative importance of these factors in relation to health effects. Generally only fine particles of dust are of health concern. Dust particles PM10 or less in size are likely to have the greatest health effects because they may be drawn deep into the lungs. Particles larger than PM10 tend to be trapped in the nose, mouth, throat or major bronchi and are typically expelled from the body. Dust particles may be termed ‘inhalable’ or ‘respirable’. Inhalable particles are usually less than PM10 and greater than PM2.5 in size. These may be deposited in the upper sections of the lungs. Respirable dust particles are less than PM2.5 and may be deposited in the lower sections of the lungs, including the alveoli.The NPI has given particulate matter of size PM10 or less a health hazard rating of 1.2 out of 3. A score of 3 represents a very high hazard to health, a score of 2 represents a medium hazard and a score of 1 is harmful to health.
The main methods for monitoring dust levels are:
Dust deposition gauges:
This method measures dust deposition rate and involves the passive deposition and capture of dust within a funnel and bottle arrangement. Data is usually collected over monthly periods and results are expressed in g/m2/month (ie. the mass of dust deposited per m² per month). This method enables determination of the relative ‘dustiness’ of sampling locations. It does not provide data on dust concentrations or enable determination of dust levels from a particular event or source. It does not give an indication of the potential health effects of the dust because it does not measure the amount of fine and very fine particles in the atmosphere.
High volume samplers:
This method determines average dust concentrations and comprises the collection of dust by drawing a constant flow rate of ambient air through a filter. Data is usually collected over a 24 hour period and results are expressed in g/m³/24hr (ie. mass of dust per volume of air per 24 hrs). A selective inlet may be fitted to a high volume sampler to restrict the particle size being sampled (for example, to ensure only PM10 particles are sampled). When coupled with a wind direction vane or matched with records of wind data, this method enables determination of dust levels from a particular event or source. It also gives an indication of the potential health effects of the dust because it allows measurement of fine and very fine particles in the atmosphere.
For more information on dust and the monitoring of dust, visit Queensland and NSW Laboratory