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

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 90 % chamber relative humidity, with subsequent analysis indicating persistence of particle bounce for sucrose aerosol of 70 nm (initial dry diameter) and α-pinene-derived SOA of number geometric mean diameters between 39 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.

A Normalized HLD (HLDN) Tool for Optimal Salt-Concentration Prediction of Microemulsions

Optimal condition-based microemulsion is key to achieving great efficiency in oil removal. One useful empirical equation to predict an optimal condition is a hydrophilic–lipophilic deviation (HLD). However, the K constants of each surfactant should be the same to combine the HLD equations for the mixed surfactant. Recently, a normalized hydrophilic-lipophilic deviation (HLDN) was presented to avoid this limitation. This work sought to determine the phase behaviors and predict the optimal salt concentrations, using HLDN for the mixed surfactant. Sodium dihexyl sulfosuccinate (SDHS) as an anionic surfactant, and alcohol alkyl polyglycol ether (AAE(6EO4PO)) as a nonionic surfactant, were both investigated. Alkanes and diesel were used as a model oil. The results showed that AAE(6EO4PO) enforced both the hydrophilic and the hydrophobic characteristics. The Winsor Type I-III transition was influenced by the ethylene oxide, while the propylene oxide presence affected the Winsor Type III-II inversion. For the HLDN equation, the average interaction term was 1.82 ± 0.86, which markedly showed a strong correlation with the fraction of nonionic surfactant in the mixed systems. The predicted optimal salt concentrations using HLDN of SDHS-AAE(6EO4PO) in the diesel systems were close to the experimental results, with an error of <10% that is significantly beneficial due to the shorter time required for optimal determination.