The generation and characterization of metallic and mixed element aerosols for human challenge studies

A spark discharge aerosol generator (Palas GFG 1000) has been utilized to generate aerosols of pure metals and of carbonaceous aerosols containing a metal component. This was achieved by fabricating metal electrodes of the desired dimensions and also by repeated instillation of saturated FeCl2 solution into a machined recess in an existing graphite electrode. Number size distributions of the resultant aerosols were measured, and field emission gun transmission electron microscopy (FEG TEM), coupled with energy dispersive X-ray (EDX) analysis, were performed on the collected samples. Whilst utilizing two identical metallic electrodes, it was found that particle-number concentration and modal diameter generally increased with a greater electrical and thermal resistivity of the electrode material. Utilizing zinc as a single electrode, or pair of electrodes, one observed an effect of enhanced airborn mass concentration of this element upon spark discharge. It is postulated that this phenomenon was due to zinc's inherent low melting and boiling points. Measurements performed with EDX analysis indicated the composition of carbon/metal aerosols to consist primarily of carbon. Aerosols generated using a stainless steel/carbon system show dense regions present, with an observed composition very close to that of stainless steel, indicating little, if any, fractionation of these particular elements during the aerosol formation process. This observation, together with evidence gained from FEG TEM imaging in further systems, suggests that droplet formation directly from the metallic electrode surface constituted an important role in the aerosol formation process.