High Temporal and Spatial Resolution Measurements of the Rapid Efflorescence of Sea Salt Droplets

Knowledge of the surface composition of sea spray aerosols (SSA) is critical for understanding and predicting climate-relevant impacts. Offline microscopy and spectroscopy studies have shown that dry supermicron SSA tend to be spatially heterogeneous particles with sodium- and chloride-rich cores surrounded by organic enriched surface layers containing minor inorganic seawater components such as magnesium and calcium. At the same time, single-particle mass spectrometry reveals several different mass spectral ion patterns, suggesting that there may be a number of chemically distinct particle types. This study investigates factors controlling single particle mass spectra of nascent supermicron SSA. Depth profiling experiments conducted on SSA generated by a fritted bubbler and total ion intensity analysis of SSA generated by a marine aerosol reference tank were compared with observations of ambient SSA observed at two coastal locations. Analysis of SSA produced by utilizing controlled laboratory methods reveals that single-particle mass spectra with weak sodium ion signals can be produced by the desorption of the surface of typical dry SSA particles composed of salt cores and organic-rich coatings. Thus, this lab-based study for the first time unifies findings from offline and online measurements as well as lab and field studies of the SSA particle-mixing state.

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Temperature-Dependent Phase Transitions of Aqueous Aerosol Droplet Systems in Microfluidic Traps

Roy

Mael

Makhnenko

et al. 2020

ACS Earth Space Chem.

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Well-mixed atmospheric aqueous aerosol droplets containing multiple chemical species can undergo processes such as liquid–liquid phase separation (LLPS) and crystallization depending on the ambient temperature and relative humidity (RH). So far, only a handful of single droplet studies have examined the effect of temperature in conjunction with the organic to inorganic ratio (OIR) on the separation RH for LLPS. In this work, we present a temperature-controlled microfluidic static trap approach to study the LLPS and efflorescence phenomenon in multiple ternary systems in a quasi-equilibrium manner. Ammonium sulfate or sodium chloride is used as the inorganic phase and 3-methylglutaric acid (3-MGA), poly(ethylene glycol), poly(propylene glycol), or poly(ethylene glycol) diacrylate is used as the organic phase. Results show a clear trend in droplets containing 3-MGA with either salt of the initial LLPS and efflorescence events occurring at higher RH at lower temperatures, while this trend is less obvious for the other organics. The organic to inorganic ratio (OIR) of the system also affected the type of first phase transition, which can be either LLPS or efflorescence. Finally, the rate of RH change also had an impact on the temperature dependence of the formation of either anhydrous or dihydrous crystals of sodium chloride upon efflorescence. These results help inform the effects of temperature, OIR, and rate of RH change on the phase state of aqueous aerosol droplets containing multiple species.

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High Temporal and Spatial Resolution Measurements of the Rapid Efflorescence of Sea Salt Droplets

Cited by 7 publications

References 24 publications

Raman Spectra of Minerals

Raman Spectra of Minerals

Effect of Structural Heterogeneity in Chemical Composition on Online Single-Particle Mass Spectrometry Analysis of Sea Spray Aerosol Particles

Temperature-Dependent Phase Transitions of Aqueous Aerosol Droplet Systems in Microfluidic Traps

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