Ultrafine particle generation through atomization technique: the influence of the solution

Aerosol particle generators represent the key devices in the complex calibration apparatus for aerosol measurement instruments. Therefore, several aerosol generation techniques were designed to produce either monodisperse and polydisperse aerosols carrying liquid and/or solid particles. In the sub-micrometer range the most reliable, repeatable (and, hence, marketed) technique is based on the atomization of a properly prepared solution. In particular, in the widely used TSI 3940 submicrometer monodisperse aerosol generator, aerosol is produced through the atomization of a solution made up of a salt in deionized distilled water. After the atomization the aerosol passed through a diffusion dryer to produce a dried polydisperse aerosol. Then, in case, a monodisperse aerosol can be selected classifying a specific particle diameter through an Electrostatic Classifier. Different solutes could be used in the solution preparation, anyway such generator system was only characterized for few solutes. In the present work the characterization of the TSI 3094 aerosol generation system was performed using different solutions in terms of both solute type and its molar concentration. In particular, different soluble salts selected mainly amongst sulfates, nitrates, carbonates and halides were considered. Moreover, molar concentrations ranging from 0.000017 to 0.017 mol L-1 were tested for each solute. Polydisperse and monodisperse aerosol measurements in terms of particle number distributions and total concentrations were performed through a Scanning Mobility Particle Sizer spectrometer (SMPS 3936, TSI) and a further Condensation Particle Counter (CPC 3075, TSI), respectively, both set (in series) downstream of the generation system. Results in terms of polydisperse aerosol characteristics (mode and total concentration) as a function of both solute type and its molar concentration were compared in order to detect solutes able to produced polydisperse aerosol showing sufficiently high concentrations in the range 5-20 nm: it usually represents the range characterized by the lowest amount of particle produced.