Ion induced nucleation based-generator of strictly singly charged (solid - liquid) polydisperse particles up to 1 μm

Abstract

Abstract: Calibration of optical counters, condensation particle counters, electrical impactors, filtration efficiency measurement, heterogeneous condensation (and many other laboratory applications in aerosol science and technology) are widely used with singly charged particles classified by a differential mobility analyzer with particles smaller than 1 μm. Nevertheless the method presents an ambiguity because of the presence of multi charged large particles of the same mobility than singly ones. This ambiguity results in uncertainty in the concentration regarded as a reference. The present paper reports a generation method of strictly singly (positive and negative) charged liquid and solid particles up to 1 μm. The generation-method is based on ion-induced nucleation of singly charged atmospheric ions. The method uses evaporation and controlled condensation of liquids or solid on seed ions. The ions grow and form wide continuum polydisperse distributions of positive or negative liquid/solid polydisperse particles up to 1 μm. The ions are produced with a corona or radioactive or soft X ray or UV source in filtered dry stream air. The final formed droplets or spheres around the ions keep the positive or negative initial charge of the ions. Vapors from low meting point solids or high boiling point and low vapor pressure liquids are used in this vaporizer-condenser generator. The paper focuses on particles with diameters up to 1 μm dedicated to classical differential mobility analyzers (DMA). The results with larger particles produced with the same generator design using heterogeneous condensation of vapors on sub 10 nm singly charged particles from melting NiCr (Kanthal) wires in air will be published in a second paper (manuscript in preparation). A companion paper on the saturation ratio profiles modeling with Comsol and comparison theory-experiments is in preparation. • Polydisperse aerosol generator based on ion induced nucleation is presented and characterized in this paper. • The generator produces particles from low melting points solids or low vapor pressure liquids. • The generator is based on evaporation-condensation method used in the widely used Sinclair Lamer generators. • Atmospheric ions produced by a corona source are used as seed residues. • Singly charged spherical particles (solid or liquid) up to 1 μm are produced by the generator without neutralizer.