Abstract. Secondary organic aerosol (SOA), formed through oxidation of volatile organic compounds (VOCs), display 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 90 %

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... ber relative humidity, with subsequent analysis indicating persistence of particle bounce for sucrose 10 aerosol of 70 nm (initial dry diameter) and α-pinene derived SOA of number geometric mean diameters between 39 nm and 136 nm (initial dry diameter). On the other hand, sucrose aerosol of 190 nm (initial dry diameter) and AS aerosol down to 70 nm (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.