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A comparison of methods to measure aerosol surface-area.

Maynard-A; Ku-B; Andresen-P; Ramachandran-G; Pai-P; Prasad-B
American Industrial Hygiene Conference and Exposition, May 8-13, 2004, Atlanta, Georgia. Fairfax, VA: American Industrial Hygiene Association, 2004 May; :17
There has been mounting evidence that for some classes of aerosols, particle surface-area is a more appropriate exposure metric than mass concentration. However, appropriate means to measure surface-area exposure within occupational settings are not widely available, and in most cases have not been evaluated extensively. Here, we present an initial comparison between four methods of measuring or estimating aerosol surface area. The four methods investigated include: surface-area derivation from particle mobility diameter measurements; estimating surface area from transmission electron microscopy (TEM) measurements; diffusion charging (using the LQ1-DC diffusion charger from Matter Engineering, Switzerland); and estimating surface-area from aerosol number and mass concentration measurements. Laboratory-generated monodisperse and polydisperse silver particles with morphologies ranging from spherical to fractal-like were used to evaluate the methods side-by-side. In addition, field data from indoor exposures to cooking smoke in India was used to compare diffusion charger measurements, and surface-area estimates from number and mass concentration measurements. Calculations of mean particle surface-area using the silver aerosol showed good agreement between the TEM, diffusion charging, and mobility diameter measurements for spherical and fractal-like monodisperse particles smaller than 100 nm. Comparisons using polydisperse aerosols were more ambiguous, but in general showed good agreement between these methods. Estimates of aerosol surface-area using number and mass concentration measurements were in general agreement with mobility diameter-derived measurements for compact particles. However, estimated surface-area was lower than anticipated for fractal-like particles. Field comparisons between the diffusion charger and the number and mass concentration-based method indicated that, with the use of a suitable calibration factor, aerosol surface-area exposure may be estimated to within a factor of 1.4 at concentrations above 500 um2/cm3. (The diffusion charger used measures concentrations up to 2000 um2/cm3, and it is expected that occupational exposures exceeding 106 um2/cm3 will not be uncommon.)
Aerosols; Aerosol-particles; Particulates; Occupational-exposure; Surface-properties; Microscopy; Silver-compounds
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Research Tools and Approaches: Exposure Assessment Methods
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American Industrial Hygiene Conference and Exposition, May 8-13, 2004, Atlanta, Georgia