Suspended Particulate Matter Definition
SPM and RSPMThere is much confusion about how to define PM10 particulate, but if articlesindicate the definitions they used then the information can be compared withinformation from other studies.
A concern is that the dust measurementequipment for PM10 particulate matter might not be designed to meet thesame defined standard as used in the articles which could lead to somediscrepancies.
Definitions of PM10 and respirable dust vary from
• Particulate Matter with diameters less than 10 micron. Not one particlecollected may be above 10 micron, regardless of shape and density.
• Particulate Matter with an aerodynamic diameter less than 10 micron. Thistakes density and shape into account.
• Particulate Matter with a d50 aerodynamic diameter of less than 10 micron.This takes density, shape and statistical averaging into account.
• Particulate Matter with a d50 aerodynamic diameter of less than 7 micron(Mining in South Africa). This is just a lower cut off used in the SouthAfrican Mining Sector of South Africa when determining respirable dustlevels on workers working on the mines.
Similar confusion exists for the PM2.5 particulate definitions and theequipment used to determine these low particle sizes need to be wellmaintained and operated by experienced people to prevent contamination ofthe samples by particulate larger than the defined size.The fact that respirable suspended particulate matter is more dangerous tohealth than larger particulate up to 100 micron is well established.
It isimportant to remember though that the ratio of RSPM to SPM will be specificto an area and the measurement of the one should be able to infer the other ifthe ratio has been experimentally determined, (excluding air pollutionmodelling).At some stage the definition should be standardised so that apples can becompared to apples. DustWatch particulate matter equipment measures SPM (suspendedparticulate matter), and is designed to have a cut-off at 100 micron, so thatthe maximum particle size collected is as close to 100 micron as possible.
The d50 of the samples is between 35 and 45 micron depending on thesampling location. This is not an aerodynamic diameter as the size isdetermined using a Malvern particle size analysis. So the d50 is the size ofparticle without taking density and shape into account.