On the Importance of Density in ELPI Data Post-Treatment
Abstract
This study compared number and mass concentrations obtained using two reference devices, a scanning mobility particle sizer (SMPS) and a tapered element oscillating microbalance (TEOM), with those calculated from raw electrical low-pressure impactor (ELPI) data. ELPI data post-treatment was performed assuming a mobility-dependent effective density and three constant densities: an average effective density, the raw material density, and the standard density (i.e., 1g/cm(3)). For the mass concentration, whatever the density considered, the ELPI-determined value was close to the reference. For the number concentration, results indicate good agreement between SMPS and ELPI number concentrations when considering effective density and, to a lesser extent, average effective density. In contrast, with the raw material density or standard density, large uncertainties in number concentration measurements were produced. A good estimation of number concentration was obtained based on ELPI data when assuming a standard density only when there was fortuitous agreement between the number tested aerosol size distribution and its mobility-dependent effective density. Thus, contrary to what some authors recommend, a standard density cannot be universally used.