Surface solvation of Martian salt analogues at low relative humidities

Kong, Xiangrui; Zhu, Suyun; Shavorskiy, Andrey; Li, Jun; Liu, Wanyu; Corral-Arroyo, Pablo; Signorell, Ruth; Wang, Sen; Pettersson, Jan B. C.

doi:10.1039/d1ea00092f

Cited by 5 publications

(12 citation statements)

References 60 publications

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“…For the magnesium (Figure d), the region (i) intensity already decreases as RH increases to 4.4%, and the change is more pronounced than observed for pure MgSO 4 at considerably higher RH (32.7%, Figure b). This implies that Mg ions in the natural salt mixture are more sensitive to water vapor than in the pure salt, in agreement with a recent report …”

Section: Resultssupporting

confidence: 93%

“…This phenomenon is not explained by the low photoionization cross-section of Na because Na has been observed in brines with low Mg 2+ content. 15 Thus, the lack of Na + detection may be due to surface depletion by the competitive Mg 2+ , as suggested by the MD results in Figure 4b. Finally, the adsorbed water molecules are preferentially in contact with the substrate and can be trapped in the interstitial spaces of the crystal structure, as shown by the red profile in Figure 4.…”

Section: Sample Characterizationmentioning

confidence: 86%

“…This implies that Mg ions in the natural salt mixture are more sensitive to water vapor than in the pure salt, in agreement with a recent report. 15 3.3. Depth Profiles.…”

Section: Sample Characterizationmentioning

confidence: 99%

“…Such phenomena may be expected to be even more relevant in natural salt substances, which have complicated ionic compositions. When water molecules start to accumulate on salt surfaces, the surfaces can be partially/fully solvated at a relative humidity (RH) well below thermodynamically predicted thresholds. − For salt mixtures that exist in nature, thermodynamics describes that water uptake occurs at lower RH than the deliquescence relative humidity (DRH) required by each pure salt component . This makes the surfaces of mixed salts extremely sensitive to water vapor .…”

Section: Introductionmentioning

confidence: 99%

“…16 This makes the surfaces of mixed salts extremely sensitive to water vapor. 15 Combined with the ion-selective surface enhancement/ depletion, the surface of mixed salts may change in their states and ionic compositions at RH much lower than conventionally expected. Moreover, some thermodynamically disfavored redox reactions have been found to occur spontaneously on a solvating salt surface.…”

Section: Introductionmentioning

confidence: 99%

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Unexpected Behavior of Chloride and Sulfate Ions upon Surface Solvation of Martian Salt Analogue

Fauré

Chen

Artiglia

et al. 2023

ACS Earth Space Chem.

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Gas-phase interactions with aerosol particle surfaces are involved in the physicochemical evolution of our atmosphere as well as those of other planets (e.g., Mars). However, our understanding of interfacial properties remains limited, especially in natural systems with complex structures and chemical compositions. In this study, a surface-sensitive technique, ambient pressure X-ray photoelectron spectroscopy, combined with molecular dynamics simulations, were employed to investigate a Martian salt analogue sampled on Earth, including a comparison with a typical sulfate salt (MgSO 4 ) commonly found on both Earth and Mars. For MgSO 4 , elemental depth profiles show that there always exists residual water on the salt surface, even at very low relative humidity (RH). When RH rises, water is well mixed with the salt within the probed depth of a few nanometers. The Cl − -and SO 4 2− -bearing Martian salt analogue surface is extremely sensitive to water vapor, and the surface layer is already fully solvated at very low RH. Unexpected ion-selective surface behavior are observed as RH rises, where the chloride is depleted, while another major anion, sulfate, is relatively enhanced when the surface becomes solvated. Molecular dynamics simulations suggest that, upon solvation with the formation of an ion-concentrated water layer adsorbed on the crystal substrate, monovalent ions experience a higher degree of dehydration than the divalent ions. Thus, to complete their first solvation shell, monovalent ions are driven away from the surface and move toward the water accumulated at the hydrophilic crystal structure.

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Section: Resultssupporting

confidence: 93%

Section: Sample Characterizationmentioning

confidence: 86%

“…This implies that Mg ions in the natural salt mixture are more sensitive to water vapor than in the pure salt, in agreement with a recent report. 15 3.3. Depth Profiles.…”

Section: Sample Characterizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Unexpected Behavior of Chloride and Sulfate Ions upon Surface Solvation of Martian Salt Analogue

Fauré

Chen

Artiglia

et al. 2023

ACS Earth Space Chem.

Self Cite

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Hygroscopic Properties of Plateau Surface Salts: Insights from Chemical Composition and Isotope Signatures

Hao,

Qiu,

et al. 2024

ACS Earth Space Chem.

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Evaporite salts from saline lakes and playas play active roles in the atmospheric cycles and the climate system, especially in the context of changing climate. This study investigates the chemical, isotopic, and hygroscopic characteristics of surface salt samples from two saline lakes, i.e., Mang’ai and Dalangtan (MA and DLT), in the Qaidam Basin. Samples from both lakes shared similar ionic compositions, with brines rich in Cl–, Mg2+, and Na+, and lakebed salts being primarily NaCl-based. Disparities in the composition between MA and DLT crust salts were observed. Isotopic analyses revealed consistent δ34S values within samples from a single site, hinting at a common origin. The sulfur source for the MA saline lake likely arises from nearby freshwater inflows and atmospheric deposits. The δ37Cl values varied by sample type, with solid samples typically exhibiting higher values than brines, attributed to 37Cl depletion during precipitation. Ionic composition largely determines hygroscopic properties. While brines started moisture absorption around 40% relative humidity (RH), lakebed salts commenced at 70% RH. The DLT playa salt, enriched in Na2SO4, demonstrated a unique behavior, responding significantly only above 80% RH. The layered DLT samples showcased variable hygroscopic behaviors, particularly the early moisture uptake of the topmost layer, despite its ionic similarity to another layer, hinting at molecular or hydration disparities. In conclusion, this investigation unravels the multifaceted relationship between salt evaporites composition and their implications for atmospheric chemistry.

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MAX IV Laboratory

Robert,

Cerenius,

Tavares

et al. 2023

Eur. Phys. J. Plus

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MAX IV Laboratory is a Swedish national synchrotron radiation facility that comprises three accelerators with varying characteristics. One of the accelerators, the 3 GeV storage ring, is the world’s first fourth-generation ring and pioneered the use of the multibend achromat lattice to provide access to ultrahigh brightness X-rays. MAX IV aims to stay at the forefront of the current and future research needs of its multidisciplinary user community, principally located in the Nordic and Baltic regions. Our 16 beamlines currently offer and continue to develop modern X-ray spectroscopy, scattering, diffraction, and imaging techniques to address scientific problems of importance to society.

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Surface solvation of Martian salt analogues at low relative humidities

Abstract: Salt aerosol plays important roles in many processes related to atmospheric chemistry and the climate systems on both Earth and Mars. Complicated and still poorly understood processes occur on the...

Cited by 5 publications

References 60 publications

Unexpected Behavior of Chloride and Sulfate Ions upon Surface Solvation of Martian Salt Analogue

Unexpected Behavior of Chloride and Sulfate Ions upon Surface Solvation of Martian Salt Analogue

Hygroscopic Properties of Plateau Surface Salts: Insights from Chemical Composition and Isotope Signatures

MAX IV Laboratory

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