Hygroscopic Properties of Saline Mineral Dust From Different Regions in China: Geographical Variations, Compositional Dependence, and Atmospheric Implications

Abstract

Saline mineral dust particles, emitted from saline topsoil in arid and semiarid regions, contribute significantly to tropospheric aerosol particles. However, hygroscopic properties of saline mineral dust particles, especially for those found in regions other than North America, are poorly understood. In this work we investigated hygroscopic properties of 13 saline mineral dust samples collected from different locations via measuring sample mass change at different relative humidity (RH; up to 90%), and measured their chemical and mineralogical compositions using ion chromatography and X‐ray diffraction. The mass growth factors at 90% RH, defined as the sample mass at 90% RH relative to that at <1% RH, were found to display large geographical variations, spanning from ~1.02 to 6.7, and the corresponding single hygroscopicity parameters (κ) were derived to be in the range of <0.01 to >1.0. The saline components (mainly Na+, Cl−, and SO42−) contained by saline mineral dust particles largely determined their hygroscopicity, and the predicted mass growth factors at 90% RH using an aerosol thermodynamic model (ISORROPIA‐II), agreed with measured values within 20% for most of samples examined, although larger discrepancies also occurred for three samples. Our results improve our understanding in hygroscopicity of saline mineral dust particles and thus their heterogeneous chemistry and ability to serve as cloud condensation nuclei to form cloud droplets.

On mineral dust aerosol hygroscopicity

“…dry mass of tenths or a few mg) as different RH under isotherm conditions. Comprehensive validation carried out confirmed the robustness of this method (Gu et al, 2017), and this instrument has been employed to study hygroscopic properties of various particles, including nonspherical particles such as saline mineral dust and pollen grains (Chen et al, 2019;Tang et al, 2019b;Tang et al, 2019c). This instrument was used in the present work to quantitatively measure hygroscopic properties of a number of mineral dust particles, including several authentic mineral dust samples from different regions in the world and individual minerals commonly found in mineral dust aerosol.…”

“…(Vlasenko et al, 2005;Sullivan et al, 2010a;Tang et al, 2016), was also investigated in our work. When received, three feldspars, dolomite, illite, chlorite and TLF dust contained significant amounts of rock chips or giant particles; as a result, they were pretreated using the procedure described in our previous work (Tang et al, 2019c). In brief, these samples were dried at 120 o C https://doi.org/10.5194/acp-2020-442 Preprint.…”

“…After centrifugalization, the solution was filtered using a 5 mL syringe fitted with a 0.2 µm PTFE membrane filter and then analyzed using ion chromatography (Metrohm model 761 Compact IC, Metrohm, Herisau, Switzerland). More information on ion chromatography analysis can be found in our previous work (Tang et al, 2019c). We attempted to measure five cations (Na + , K + , NH4 + , Mg 2+ and Ca 2+ ) and seven anions (NO3 -, SO4 2-, Cl -, NO2-, Br -, Fand PO4 3-), and their detection limits were estimated to be around 0.02 mg/L.…”

“…Tables 2-5 summarize mw/m0 and θ as a function of RH for all the mineral dust examined in our work. Please note that our previous work (Tang et al, 2019c) discussed water uptake by China loess and QH dust, and these results are included here to compare with the other nineteen mineral dust samples.…”

“…including China loess, QH dust and TLF dust. It should be pointed out that mw/m0 have been reported in our previous work (Tang et al, 2019c) for China loess and QH dust, and they are included here for comparison. As shown in Table 5, the three Asian authentic dust samples exhibited very similar water uptake properties, and their mw/m0 were determined to be 0.021-0.022 at 90% RH.…”