Freshman chemistry teaches that Fe 3+ and Cu 2+ ions are stable in water solutions, but their reduced forms, Fe 2+ and Cu + , cannot exist in water as the major oxidation state due to the fast oxidation by O 2 and/or disproportionation. Contrary to these well-known facts, significant fractions of dissolved Fe and Cu species exist in their reduced oxidation states in atmospheric water such as deliquesced aerosols, clouds, and fog droplets. Current knowledge attributes these phenomena to the stabilization of the lower oxidation states by the complexation of ligands and the various photochemical or thermal pathways that can reduce the higher oxidation states. In this study, by spraying the water solutions of transition metal ions into microdroplets, we show the results of the spontaneous reduction of ligated Fe(III) and Cu(II) species into Fe(II) and Cu(I) species, presenting a previously unknown source of reduced transition metal ions in atmospheric water. It is the spontaneously generated electrons in water microdroplets that are responsible for the reduction. Control experiments in the atmosphere and in a glove box filled with precisely controlled gaseous contents reveal that O 2 , CO 2 , and NO 2 are the major competitors for the electrons, forming O 2 − , HCO 2 − , and NO 2 − , respectively. Taking these findings together, we opine that microdroplet chemistry might play significant but previously underestimated roles in atmospheric redox chemistry.

Atomic and molecular iodine, I• and I2, play important roles in the atmosphere, such as the catalytic depletion of ozone and the oxidation of gaseous elemental mercury. It’s known that...

The development of efficient, low-cost, easy-to-use ambient ionization methods has been a major goal of modern mass spectrometry. In this Letter, we present a gas-free, voltage-free, economic, and safe desorption ionization method using the plasma generated by a radioactive element, americium-241, scavenged from smoke detectors that equip almost every household. No other energy sources, such as laser, discharge, fast-moving carrier gas, solvent droplet, ultrasound, or heat are needed. We name this new method as americium-241 desorption ionization (AmDI). AmDI is tested for the detection of more than 20 volatile and nonvolatile chemicals under different sampling conditions, and the detection limit can be in the range of tens of picograms for some analytes. Mechanistically, we provide evidence that the α particles emitted from radioactive decay ionize ambient air, and the resulting plasma further energizes and ionizes the surface analytes for mass spectrometry detection. We anticipate wide applications of AmDI in mass spectrometric sampling in the near future because of the plethora of merits.

Chemical equilibrium contains information on the extent of reaction, which is an important part of physical chemistry. In the context of the solvation of lithium polysulfide in lithium-sulfur batteries, Q4-9 of the 54th International Chemical Olympiad (IChO) examined students' understanding and calculation of the apparent equilibrium constant of the reaction in the equilibrium system of multi conformational compounds. This article will discuss how to apply the weighted average of the free energy of the two conformations of lithium polysulfide to calculate the apparent equilibrium constant from the perspective of thermodynamics and statistical physics.

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