This report describes work carried out in order to determine which metric for very small particles best relates the exposure measurement to the health risk posed by them.
An experimental rig was constructed in which it was possible to expose three instruments, simultaneously, to aerosols generated in a range of concentrations. These aerosols contained ultrafine particles of different chemical composition and particle shape. The relationships between the mass, number and active surface area of these particles, and how they are affected by characteristics such as chemical composition and morphology for these instruments were investigated.
Consistent relationships were found for mass and active surface area with increasing number concentrations for the particle sizes investigated, but they were not consistent with size. The influence of particle morphology on the relationship between mass, number and surface area, was not significant for polydisperse ultrafine aerosols and the degree of agglomeration was more likely to be responsible for the inconsistency of instrument response to size. No simple relationship was found for predicting active surface area and mass from the results of size and number measurements. The findings indicated it is unlikely that nanoparticles will be present in a working environment in an unattached state.
This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author alone and do not necessarily reflect HSE policy.
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