Evaluation of different techniques for particle size distribution measurements on laser-generated aerosols

Knowledge about aerosol particle sizes in laser-generated aerosols is required to better understand nonstoichiometric effects as they occur during laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). However, published particle size distributions measured by different techniques provide an inconclusive picture, since measurements base on different physical properties of a particle. This is especially the case for the size determination of agglomerated nano-particles, which contribute significantly to the total particle mass transported to the ICP. While their aerodynamic diameters measured by particle impaction are always smaller than the volume equivalent ones (d(a)<d(ve)), electrical mobility diameters determined by differential mobility analyses (DMA) are significantly larger than the corresponding volume equivalent diameters (d(m)>d(ve)). This leads to large discrepancies between measured d(a) and d(m) values, which is shown within this work on brass aerosols generated by laser ablation. Results of light scattering measurement, which is a quick and simultaneous method, show particle diameters in between impaction and DMA data. However, it is important to know that the different methods are not in contradiction to each other, but measure specific physical properties of a particle and complement each other. Results of this study demonstrate the advantages and limitations of the individual particle size measurement techniques and should be seen as guidance to select the adequate technique for laser generated aerosol particle size determinations.