Direct measurements of HOx radicals in the marine boundary layer: testing the current tropospheric chemistry mechanism

OH and HO(2) radicals, atmospheric detergents, and the reservoir thereof, play central roles in tropospheric chemistry. In spite of their importance, we had no choice but to trust their concentrations predicted by modeling studies based on known chemical processes. However, recent direct measurements of these radicals have enabled us to test and revise our knowledge of the processes by comparing the predicted and observed values of the radical concentrations. We developed a laser-induced fluorescence (LIF) instrument and successfully observed OH and HO(2) at three remote islands of Japan (Oki Island, Okinawa Island, and Rishiri Island). At Okinawa Island, the observed daytime level of HO(2) agreed closely with the model estimates, suggesting that the photochemistry at Okinawa is well described by the current chemistry mechanism. At Rishiri Island, in contrast, the observed daytime level of HO(2) was consistently much lower than the calculated values. We proposed that iodine chemistry, usually not incorporated into the mechanism, is at least partly responsible for the discrepancy in the results. At night, HO(2) was detected at levels greater than 1 pptv at all three islands, suggesting the presence of processes in the dark that produce radicals. We showed that ozone reactions with unsaturated hydrocarbons, including monoterpenes, could significantly contribute to radical production.     

Solid particle in the boundary layer of a rising bubble

The hydrodynamic interaction of a solid particle and the boundary layer around a rising bubble is analyzed in the before-contact state (BCS) of a flotation act. The lagging of the particle behind the basic outer flow is accounted for. The forces acting on the particle are qualitatively examined. A new term is introduced in the force balance — the migration force. An expression for the collision efficiency is proposed that concerns a particle already entrained in the bubbles boundary layer.     

Prediction of daytime variations of HO2 radical concentrations in the marine boundary layer using BP network

A Back-Propagation Neural Network (BPNN) was established to predict the daytime variations of HO₂ radical concentration observed in the field campaign RISFEX 2003 (RIShiri Fall Experiment 2003) conducted in September 2003 at Rishiri Island (45.07 N, 141.12 E, and 35m asl) in the Sea of Japan. The initial weight matrices and bias vectors for the network were optimized by a bee evolutionary genetic algorithm (BEGA). It was found that the input variables sensitive to HO₂ variation were photolysis frequency of O₃ to O(¹D) (J(O¹D)), a composite parameter defined as the ratio of HC to NO _x reactivity towards OH radicals (Φ), and the total aerosol surface area (A). The predicted results are closely correlated with the experimental data with the coefficient of determination (R ²) close to 1. In addition, the means and ranges of the predicted HO₂ concentration agree with the observed data with the correlation coefficient (R), the index of agreement (IA) and the fractional bias (FB) in the range of 0.84–0.93, 0.88–0.95 and ?14%–7%, respectively. This study demonstrates that BPNN is a potential tool to predict the daytime variations of HO₂ radical concentrations in the marine boundary layer (MBL).     

Incoherent broad-band cavity-enhanced absorption spectroscopy of the marine boundary layer species I2, IO and OIO

The novel combination of incoherent broad-band cavity-enhanced absorption spectroscopy (IBBCEAS) and a discharge-flow tube for the study of three key atmospheric trace species, I(2), IO and OIO, is reported. Absorption measurements of I(2) and OIO at lambda=525-555 nm and IO at lambda=420-460 nm were made using a compact cavity-enhanced spectrometer employing a 150 W short-arc Xenon lamp. The use of a flow system allowed the monitoring of the chemically short-lived radical species IO and OIO to be conducted over timescales of several seconds. We report detection limits of approximately 26 pmol mol(-1) for I(2) (L=81 cm, acquisition time 60 s), approximately 45 pmol mol(-1) for OIO (L=42.5 cm, acquisition time 5 s) and approximately 210 pmol mol(-1) for IO (L=70 cm, acquisition time 60 s), demonstrating the usefulness of this approach for monitoring these important species in both laboratory studies and field campaigns.     

TTA as a potential hole transport layer for application in conventional polymer solar cells

Hole transport layers(HTLs) play a vital role in organic solar cells(OSCs). In this work, a derivative of tetrathiafulvalene with four carboxyl groups TTA was introduced as a novel HTL to fabricate OSC with high performance. Displaying a better energy level match between HTL and active layers, the TTA based devices show a peak power conversion efficiency of 9.09%, which is comparable to the devices based on PEDOT:PSS. The favorable surface morphology recorded via atomic force microscopy, low series loss and charge recombination indicated by electrochemical impedance spectroscopy, synchronously verify the potential of TTA for application in OSCs as a valid kind of HTLs.     

The potential of MXene materials as a component in the catalyst layer for the Oxygen Evolution Reaction

MXenes are a class of 2D/layered materials which are highly conductive, hydrophilic, have a large electrochemical surface area and are easily processible into electrodes for energy applications. Since the discovery of MXenes over ten years ago, these materials have been mainly used in the preparation of electrodes for batteries and supercapacitors. However, due to their aforementioned properties, MXenes could potentially be utilised as a component in the catalyst layer for the Oxygen Evolution Reaction (OER). This opinion piece will discuss some of the recent literature in the area of hybrid catalysts consisting of various Transition Metal Oxides (TMOs) and MXenes for the OER. We will also discuss current drawbacks and future outlook in this new area of research.     

Photochemical production of ozone in marine boundary layer in the sea of Japan: Results of the Rishiri Fall Experiment campaign

The Rishiri Fall Experiment (RISFEX ) campaign was performed in September 2003 at Rishiri island (45.07 N, 141.12 E, and 35 m asl) in the sea of Japan to investigate photochemical production of ozone in the marine boundary layer. Total peroxy radicals RO _x (HO₂ + RO₂) and NO _x (NO + NO₂) were measured together with other chemical species and physical parameters relevant to ozone production. The ozone production rate (P(O₃)) was estimated from measured peroxy radicals and was found to be highly variable between days, with 30-min averaged midday values varying from 0.2 to 1.7 ppbv/h (ppbv refers to part per billion by volume). The daytime mean P(O₃) for the air masses from relatively clean NE sector is close to zero, but significantly higher for air masses from more polluted W and SE sector, suggesting the impact of transport of pollutants on the remote local ozone production. The experimentally determined P(O₃) is compared with those derived from a time-dependent box model based on Regional Atmospheric Chemistry Modeling (RACM), and both the methods give the results generally in agreement. The model calculation shows that HO₂ + NO reaction contributes most to ozone production, ca. 60% at midday, followed by the reactions of CH₃O₂ and ISOP (peroxy radicals formed from isoprene) with NO which account for ca. 13% and 10% to ozone production, respectively, at noon. Sensitivity analysis indicates that the ozone production during the measurement period is within NO _x -limited regime.     

Simultaneous particle and vapor deposition in a laminar boundary layer

A number of industrial and technical applications involve simultaneous particle and vapor deposition from a hot gas onto cold surfaces. For example, deposition of particles and corrosive vapors reduces the lifetime of heat exchangers in power plants and in blades of gas turbines. On another hand, in the OVD (outside vapor deposition) process used in manufacturing optical fibers, a controlled deposition of silica particles and dopant vapors is necessary for obtaining products with prescribed characteristics. In the present paper, a detailed mathematical and numerical model of this process is developed for the flow region near a stagnation point of a two-dimensional body, such as a cylinder. Using an inverse scavenging factor as a small parameter, an analytical asymptotic solution is found for vapor distribution in a condensation layer adjacent to the surface. The results of numerical calculations are presented in the form of surface temperature dependencies of dimensionless deposition rates and profiles of physical parameters of the system at a wide range of surface/gas temperature ratios.     

Electrochemical deposition of a copper carboxylate layer on copper as potential corrosion inhibitor

Carboxylic acids and sodium carboxylates are used to protect metals against aqueous and atmospheric corrosion. In this paper, we describe the application of a layer of copper carboxylate on the surface of a copper electrode by means of cyclic voltammetry technique and tests which measure the corresponding resistance to aqueous corrosion. Unlike the soaking process, which also forms a film on the surface, the use of cyclic voltammetry allows one to follow the deposition process of the copper carboxylates onto the electrode. The modified electrodes have been characterised with infrared spectroscopy. In addition, the corrosion resistance of the film has been investigated using polarisation resistance and Tafel plot measurements.     

Sodium periodate as a primary oxidant for water-oxidation catalysts

Sodium periodate was characterized as a primary chemical oxidant for the catalytic evolution of oxygen at neutral pH using a variety of water-oxidation catalysts. The visible spectra of solutions formed from Cp*Ir(bpy)SO(4) during oxygen-evolution catalysis were measured. NMR spectroscopy suggests that the catalyst remains molecular after several turnovers with sodium periodate. Two of our [Cp*Ir(bis-NHC)][PF(6)](2) complexes, along with other literature catalysts, such as the manganese terpyridyl dimer, Hill's cobalt polyoxometallate, and Meyer's blue dimer, were also tested for activity. Sodium periodate was found to function only for water-oxidation catalysts with low overpotentials. This specificity is attributed to the relatively low oxidizing capability of sodium periodate solutions relative to solutions of other common primary oxidants. Studying oxygen-evolution catalysis by using sodium periodate as a primary oxidant may, therefore, provide preliminary evidence that a given catalyst has a low overpotential.     

Mechanical properties of the boundary lubrication layer

The two-term friction law is presented in a form following from its derivation on the basis of the effect of molecular forces close to the short- and long-range forces. This proves its heuristic significance. The boundary friction mechanism is described, in particular that applicable to the theory of sliding on ice. This theory was substantiated strictly quantitatively. In conclusion, the problem is formulated on the side of the transition from the viscous mode of a lubricating layer to the boundary lubrication mode.     

Thermal boundary layer in a gas subject to a time dependent pressure

An analysis of the thermal boundary layer in a gas subject to time dependent pressure variations has been made for the case in which the thermal conductivity is proportional to the temperature. Explicit expressions for the time dependent boundary layer profile, the displacement thickness and the heat transfer rate are presented.     

Measurements in a thermal laminar boundary layer with a constant pressure gradient

Mean temperature profiles in a laminar boundary layer which develops with a constant favourable pressure gradient over a constant temperature smooth surface have been measured and are in reasonable agreement with numerical solutions of the boundary layer equations.     

2-Iodoxybenzoic acid--a simple oxidant with a dazzling array of potential applications

Since its discovery by Christoph Hartmann and Victor Meyer in 1893, 2-iodoxybenzoic acid (IBX) has emerged as a rather ubiquitous oxidant for organic synthesis. The past decade has seen the development of a large variety of applications that go far beyond the simple oxidation of alcohols. This Review is concerned with the synthetic potential of IBX, with particular emphasis on uncommon reactivity patterns and novel fields of application.     

Spectroscopic analysis of the tribological behavior of a model boundary layer lubricant

Highly ordered alkanethiol self-assembled monolayers (SAMs) on gold substrates are suitable models of boundary layer lubricants and may be used in actual nanoscale device applications. Here, such monolayers were studied by spectroscopic methods as a function of tribological wear (rubbing) using a pin-on-disk microtribometer. The coefficient of friction (COF) (ratio of the frictional force to the load) was measured with the tribometer, and reflectance infrared spectra and X-ray photoelectron spectra were obtained as the monolayer film failed and the COF changed. The results show that it is possible to correlate disorder in the monolayer film with tribological failure of the film, and that continued rubbing produces a chemical change in the monolayer film. Disorder in the monolayer is distinct from the influence of wear in the underlying gold substrate. Aged SAMs, having sulfonate rather than thiol headgroups and initially less well ordered, behave differently to the well-ordered freshly prepared SAMs. Interestingly, they show a lower COF over many more cycles of exposure to the rubbing pin. The impact of the mechanism of film failure in boundary layer lubrication is discussed.