A Review on the Bulk and Surface Chemistry of Iron in Atmospherically-relevant Systems Containing Humic Like Substances (HULIS)

As the fourth most abundant element by mass in the Earth’s crust, iron is ubiquitous and its chemistry is rich and interdisciplinary in nature. This review synthesizes the current state of knowledge of iron chemistry in multicomponent atmospheric aerosols, which is also applicable to other atmospherically-relevant systems that include iron-containing anthropogenic nanodust, ocean surfaces and buildings. Because of the abundance of humic-like substances (HULIS) in these systems, studies on their chemistry with iron and those used as models for HULIS are the focus of this review. Findings from field measurements and laboratory studies are summarized to highlight major themes in iron chemical reactivity that varies depending on the solubility, redox conditions, absence and presence of UV-visible light and reactive oxygen species, pH, and temperature. The review also highlights key differences between bulk and surface chemistry of iron-containing materials, which varies considerably because of the structure of interfacial water and solvent cage effect. Additional laboratory, field, and modeling studies are needed to better understand the contributions of transition metals chemistry to secondary organic aerosol formation and chemistry, uptake, and release of trace gas phase species. This information will improve the predictive power of models that incorporate aerosols chemistry and physics

Step Detection Algorithm For Accurate Distance Estimation Using Dynamic Step Length

In this paper, a new Smartphone sensor based algorithm is proposed to detect accurate distance estimation. The algorithm consists of two phases, the first phase is for detecting the peaks from the Smartphone accelerometer sensor. The other one is for detecting the step length which varies from step to step. The proposed algorithm is tested and implemented in real environment and it showed promising results. Unlike the conventional approaches, the error of the proposed algorithm is fixed and is not affected by the long distance. Keywords distance estimation, peaks, step length, accelerometer.Comment: this paper contains of 5 pages and 6 figure

Dark Iron-Catalyzed Reactions in Acidic and Viscous Aerosol Systems Efficiently Form Secondary Brown Carbon

Iron-driven secondary brown carbon formation reactions from water-soluble organics in cloud droplets and aerosols create insoluble and soluble products of emerging atmospheric importance. This work shows, for the first time, results on dark iron-catalyzed polymerization of catechol forming insoluble black polycatechol particles and colored water-soluble oligomers under conditions characteristic of viscous multicomponent aerosol systems with relatively high ionic strength (I = 1–12 m) and acidic pH (∼2). These systems contain ammonium sulfate (AS)/nitrate (AN) and C3–C5 dicarboxylic acids, namely, malonic, malic, succinic, and glutaric acids. Using dynamic light scattering (DLS) and ultra high pressure liquid chromatography-mass spectrometry (UHPLC-MS), we show results on the rate of particle growth/agglomeration and identity of soluble oligomeric reaction products. We found that increasing I above 1 m and adding diacids with oxygen-to-carbon molar ratio (O:C \u3e 1) significantly reduced the rate of polycatechol formation/aggregation by a factor of 1.3 ± 0.4 in AS solution in the first 60 min of reaction time. Using AN, rates were too slow to be quantified using DLS, but particles formed after 24 h reaction time. These results were explained by the relative concentration and affinity of ligands to Fe(III). We also report detectable amounts of soluble and colored oligomers in reactions with a slow rate of polycatechol formation, including organonitrogen compounds. These results highlight that brown carbon formation from iron chemistry is efficient under a wide range of aerosol physical states and chemical composition

Reactivity of aminophenols in forming nitrogen-containing brown carbon from iron-catalyzed reactions

Nitrogen-containing organic carbon (NOC) in atmospheric particles is an important class of brown carbon (BrC). Redox active NOC like aminophenols received little attention in their ability to form BrC. Here we show that iron can catalyze dark oxidative oligomerization of o- and p-aminophenols under simulated aerosol and cloud conditions (pH 1–7, and ionic strength 0.01–1 M). Homogeneous aqueous phase reactions were conducted using soluble Fe(III), where particle growth/agglomeration were monitored using dynamic light scattering. Mass yield experiments of insoluble soot-like dark brown to black particles were as high as 40%. Hygroscopicity growth factors (κ) of these insoluble products under sub- and super-saturated conditions ranged from 0.4–0.6, higher than that of levoglucosan, a prominent proxy for biomass burning organic aerosol (BBOA). Soluble products analyzed using chromatography and mass spectrometry revealed the formation of ring coupling products of o- and p-aminophenols and their primary oxidation products. Heterogeneous reactions of aminophenol were also conducted using Arizona Test Dust (AZTD) under simulated aging conditions, and showed clear changes to optical properties, morphology, mixing state, and chemical composition. These results highlight the important role of iron redox chemistry in BrC formation under atmospherically relevant conditions

Rapid Surface Oxidation as a Source of Surface Degradation Factor for Bi2Se3

Bi2Se3 is a topological insulator with metallic surface states residing in a large bulk bandgap. It is believed that Bi2Se3 gets additional n-type doping after exposure to atmosphere, thereby reducing the relative contribution of surface states in total conductivity. In this letter, transport measurements on Bi2Se3 nanoribbons provide additional evidence of such environmental doping process. Systematic surface composition analyses by X-ray photoelectron spectroscopy reveal fast formation and continuous growth of native oxide on Bi2Se3 under ambient conditions. In addition to n-type doping at the surface, such surface oxidation is likely the material origin of the degradation of topological surface states. Appropriate surface passivation or encapsulation may be required to probe topological surface states of Bi2Se3 by transport measurements

Investigation of the synthesis, activation, and isosteric heats of CO₂ adsorption of the isostructural series of metal-organic frameworks M₃(BTC)₂ (M = Cr, Fe, Ni, Cu, Mo, Ru)

The synthesis, activation, and heats of CO₂ adsorption for the known members of the M₃(BTC)₂ (HKUST-1) isostructural series (M = Cr, Fe, Ni, Zn, Ni, Cu, Mo) were investigated to gain insight into the impact of CO₂–metal interactions for CO₂ storage/separation applications. With the use of modified syntheses and activation procedures, improved BET surface areas were obtained for M = Ni, Mo, and Ru. The zero-coverage isosteric heats of CO₂ adsorption were measured for the Cu, Cr, Ni, Mo, and Ru analogues and gave values consistent with those reported for MOFs containing coordinatively unsaturated metal sites, but lower than for amine functionalized materials. Notably, the Ni and Ru congeners exhibited the highest CO₂ affinities in the studied series. These behaviors were attributed to the presence of residual guest molecules in the case of Ni₃(BTC)₂(Me₂NH)₂(H₂O) and the increased charge of the dimetal secondary building unit in [Ru₃(BTC)₂][BTC].Massachusetts Institute of Technology. Energy Initiative (Seed Fund

Open questions on transition metals driving secondary thermal processes in atmospheric aerosols

Transition metals are increasingly recognized as key drivers in the formation and aging of light-absorbing organic aerosols, known as brown carbon, which impact the energy flux in the atmosphere. Here the authors discuss somewhat overlooked condensed phase chemical processes and identify research needs to improve our fundamental understanding of atmospheric aerosols and ultimately reduce modelling uncertainties of the direct and indirect effects of aerosol particles on the climate