Heterogeneous Reactions of HX + HONO and I2on Ice Surfaces: Kinetics and Linear Correlations

MnO2-Induced Oxidation of Iodide in Frozen Solution

Metal oxides play a critical role in the abiotic transformation of iodine species in natural environments. In this study, we investigated iodide oxidation by manganese dioxides (β-MnO₂, γ-MnO₂, and δ-MnO₂) in frozen and aqueous solutions. The heterogeneous reaction produced reactive iodine (RI) in the frozen phase, and the subsequent thawing of the frozen sample induced the gradual transformation of in situ-formed RI to iodate or iodide, depending on the types of manganese dioxides. The freezing-enhanced production of RI was observed over the pH range of 5.0-9.0, but it decreased with increasing pH. Fulvic acid (FA) can be iodinated by I^-/MnO₂ in aqueous and frozen solutions. About 0.8-8.4% of iodide was transformed to organoiodine compounds (OICs) at pH 6.0-7.8 in aqueous solution, while higher yields (10.4-17.8%) of OICs were obtained in frozen solution. Most OICs generated in the frozen phase contained one iodine atom and were lignin-like compounds according to Fourier transform ion cyclotron resonance/mass spectrometry analysis. This study uncovers a previously unrecognized production pathway of OICs under neutral conditions in frozen environments.

The effect of (H2O)n (n = 1-3) clusters on the reaction of HONO with HCl: a mechanistic and kinetic study

The reaction between HONO and HCl is a possible pathway for the generation of ClNO, which is prone to photolyze, produce chlorine radicals, and accelerate the oxidation of tropospheric VOCs. Current experimental and theoretical studies have significant differences in rate constants under similar conditions. This study aims to examine the reasons for this difference. In this study, the effects of a single water molecule, water dimer, water trimer, excess HCl and excess HONO on the reaction mechanism of HONO + HCl were studied at the CCSD(T)/aug-cc-pVTZ//M06-2X/6-311+G(2df,2p) level and the rate constants of each reaction channel were calculated. Our results showed that the reaction potential barrier of HONO with HCl was the lowest only when the water dimer was present, and the reaction rate constants were close to the experimental results, and both the cis-HONO⋯(H₂O)₂ + HCl and the trans-HONO⋯(H₂O)₂ + HCl reaction paths are likely to occur. We think that the reason for the inconsistency between experimental and theoretical results is that the water dimer is involved in the reaction in experiments.

Production of Molecular Iodine and Tri-iodide in the Frozen Solution of Iodide: Implication for Polar Atmosphere

The chemistry of reactive halogens in the polar atmosphere plays important roles in ozone and mercury depletion events, oxidizing capacity, and dimethylsulfide oxidation to form cloud-condensation nuclei. Among halogen species, the sources and emission mechanisms of inorganic iodine compounds in the polar boundary layer remain unknown. Here, we demonstrate that the production of tri-iodide (I3(-)) via iodide oxidation, which is negligible in aqueous solution, is significantly accelerated in frozen solution, both in the presence and the absence of solar irradiation. Field experiments carried out in the Antarctic region (King George Island, 62°13'S, 58°47'W) also showed that the generation of tri-iodide via solar photo-oxidation was enhanced when iodide was added to various ice media. The emission of gaseous I2 from the irradiated frozen solution of iodide to the gas phase was detected by using cavity ring-down spectroscopy, which was observed both in the frozen state at 253 K and after thawing the ice at 298 K. The accelerated (photo-)oxidation of iodide and the subsequent formation of tri-iodide and I2 in ice appear to be related with the freeze concentration of iodide and dissolved O2 trapped in the ice crystal grain boundaries. We propose that an accelerated abiotic transformation of iodide to gaseous I2 in ice media provides a previously unrecognized formation pathway of active iodine species in the polar atmosphere.

Kinetics and products of heterogeneous reaction of HONO with Fe2O3 and Arizona Test Dust

Kinetics and products of the reaction of HONO with solid films of Fe2O3 and Arizona Test Dust (ATD) were investigated using a low pressure flow reactor (1 - 10 Torr) combined with a modulated molecular beam mass spectrometer. The reactive uptake of HONO was studied as a function of HONO concentration ([HONO]0 = (0.6 - 15.0) × 10(12) molecules cm(-3)), relative humidity (RH = 3 × 10(-4) - 84.1%) and temperature (T = 275 - 320 K). Initial reactive uptake coefficients were found to be similar under dark conditions and in the presence of UV irradiation (JNO2 = 0.012 s(-1)) and independent of the HONO concentration and temperature. In contrast, the relative humidity (RH) was found to have a strong impact on the uptake coefficients: γ (ATD) = 3.8 × 10(-6) (RH)(-0.61) and γ (Fe2O3) = 1.7 × 10(-6) (RH)(-0.62) (γ calculated with BET surface area, 30% conservative uncertainty). In both reactions of HONO studied, NO2 and NO were observed as gaseous products with yields of (60 ± 9) and (40 ± 6) %, respectively, independent of relative humidity, temperature, concentration of HONO and UV irradiation intensity. The observed data point to minor importance of the HONO uptake on mineral aerosol compared with other known sinks of HONO in the atmosphere, which are its dry deposition and photolysis in night-time and during the day, respectively.

One more type of extrathermodynamic relationship

A new type of extrathermodynamic relationship is presented: DeltaH = Ti[DeltaS + R Delta(ln Omega)] + beta, where Omega is the phase volume and beta is a constant. This type of relationship holds for a series of systems in the case where deltaDelta(ln Omega) is changeable. The relation between this type of correlation and linear free-energy relationships is shown. An example of the specified correlation for energy parameters of excimers forming in different dipyrenylalkanes is demonstrated.