Utilizing an electrical low-pressure impactor to indirectly probe water uptake via particle bounce measurements

Abstract

Secondary organic aerosol (SOA), formed through oxidation of volatile organic compounds (VOCs), displays complex viscosity and phase behaviors influenced by temperature, relative humidity (RH), and chemical composition. Here, the efficacy of a multi-stage electrical low-pressure impactor (ELPI) for indirect water uptake measurements was studied for ammonium sulfate (AS) aerosol, sucrose aerosol, and α-pinene-derived SOA. All three aerosol systems were subjected to greater than 90g% chamber relative humidity, with subsequent analysis indicating persistence of particle bounce for sucrose aerosol of 70gnm (initial dry diameter) and α-pinene-derived SOA of number geometric mean diameters between 39 and 136gnm (initial dry diameter). On the other hand, sucrose aerosol of 190gnm (initial dry diameter) and AS aerosol down to 70gnm (initial dry diameter) exhibited no particle bounce at elevated RH. Partial drying of aerosol within the lower diameter ELPI impaction stages, where inherent and significant RH reductions occur, is proposed as one explanation for particle bounce persistence.