Humidity-dependent viscosity and hygroscopicity after aging with SO₂ of biomass burning single nanoparticle

Although understanding the physicochemical properties of nanoparticles is essential to studying their impact on climate and health, information on the viscosity of nanoparticles composed of organic and inorganic salts, as well as the aging process with soluble polluting gases is still rare. In this work, based on a high contrast imaging device enabled by the photonic chip, we measured the hygroscopic growth factors (GFs) of nanoparticles of KCl and glucose mixed in different organic and inorganic dry mass ratios (OIRs). In addition, we also proposed a viscosity retrieval method to quantify the viscosity of the nanoparticles at different relative humidities (RHs) according to the Arrhenius mixing rule and Zdanovskii-Stokes-Robinson approach. Moreover, the retrieval viscosities after deliquescence are almost in perfect agreement with the predicted curves from the Aerosol Inorganic-Organic Mixtures Functional groups Activity Coefficients Viscosity model. Furthermore, the hygroscopic GFs of the components other than glucose in the aged mixed-component particles after deliquescence is slightly higher than that of the aged single component KCl. This might be due to the viscosity of the organic components cause a delay in the volatilization of HCl gas and the formation of K₂SO₄. For instance, the calculated GFs for the aged mixtures with OIRs of 1:3,1:1 and 3:1 are 1.61, 1.62 and 1.66 at 90 % RH, respectively, while the GF of the aged single component KCl is about 1.60. These results are expected to provide theoretical reference for the future field observation of the various physicochemical property of ambient aerosol samples.